Under the Oak Tree Vol 3 by Suji Kim

Here is a summary with spoilers for Under the Oak Tree Vol 3 by Suji Kim

The Remdragon Knights begin traveling to Livadon as part of the coalition army's campaign against the monsters. Maximilian Calypse, known as Maxi, travels with Riftan and the knights but is not permitted to accompany them into the main fighting. Riftan takes her to a monastery where she is supposed to remain safely behind the front lines while the knights continue toward the battlefield. Maxi hates being left behind, particularly because she has already developed considerable magical and healing abilities and believes she can contribute. Riftan insists that the monastery is the safest place for her. The official description specifically identifies this separation as the starting point of the volume: Riftan rides to war while Maxi remains at the monastery caring for civilians.

At the monastery, Maxi works with the other noblewomen and clerics to treat villagers and wounded people. Rather than simply waiting for Riftan, she becomes involved in the medical work and uses the healing magic she has learned. She is constantly worried about the campaign, especially because the monster army has already demonstrated that it can outmaneuver human forces. Her anxiety increases whenever there is no news from the front. She also knows that Riftan is likely to be placed in the most dangerous positions because he is the commander of the Remdragon Knights and one of the strongest warriors in the coalition.

Maxi eventually becomes unable to tolerate remaining at the monastery while Riftan is fighting. She disguises herself and leaves the monastery so she can reach the battlefield and help as a healer. Her decision directly violates Riftan's instructions. She joins the support forces moving toward the front and begins treating soldiers while attempting to remain hidden from the Remdragon Knights. Her disguise works for a time because the battlefield is crowded with soldiers, healers, mages, and refugees. The longer she remains there, however, the more dangerous her situation becomes. Soon she decides she wants to see Riften from afar, but ends up running right into him. He is furious when he finds out what she has done, has to leave to cool off. The next days are tense for the two of them. 

The Livadon campaign becomes increasingly violent. The coalition forces discover that the monsters are using tactics rather than simply attacking randomly. The army eventually moves toward Vesmore, a walled city that has fallen under the control of the monsters. Riftan leads the assault while other Remdragon Knights command separate units. Maxi remains with the support forces and uses defensive and healing magic whenever she can. During the campaign she becomes more confident in her ability to use magic in an actual battle rather than only in controlled training situations.

The coalition eventually launches a major attack on Vesmore. Cavalry from Wedon and Dristan charge the monster forces while the Remdragon Knights lead the assault. Maxi watches from the support area as Riftan and the other knights break through the enemy lines. The monster army includes enormous creatures and undead-like enemies, and the fighting is severe. Maxi's role becomes increasingly dangerous because the distinction between the rear support area and the battlefield disappears as the fighting spreads. The official publisher excerpt confirms that the campaign involves both the coalition's military assault and large numbers of monsters.

While at the camp, things are still tense between Riftan and Maxi. Maxi goes out into the camp and runs into another general. The two have an interaction that puts a stain on Riftan. It turns into a fight and Riftan shows up to defend his honor and his wife. He promises retribution when the war ends. Riftan than realzies he needs to get his wife out of the camp. Though that night they do recconect sexually, the first time in a whilel; though Riftan is still mad at Maxi. Riftan than commands the campaign to move, and then he has a few, including Maxi, go off on a side quest. Though Maxi soon finds out it is because there is a fort close by that she should be safe at. 

During the campaign and traveling to the form, Maxi repeatedly pushes her mana beyond what her body can safely sustain; especially when they are attacked. She uses powerful defensive magic to protect the soldiers around her and eventually performs an especially dangerous act involving a massive boulder. She uses her magic to prevent the rock from crushing the forces below, but the effort severely depletes her mana. She collapses afterward and is left in extremely poor physical condition. The people around her believe that she has saved them and treat her as a hero, but Maxi herself feels guilty because she knows that she acted recklessly and endangered herself.

The coalition army eventually gains the upper hand. The monster commander and tactician are defeated, causing the monster army to lose much of its organization. A large number of trolls remain farther north, but the main invasion is beginning to collapse. Maxi is too weak to participate further. She is placed under the care of healers and clerics while the army finishes the campaign. Riftan is furious when he discovers what she has done, but his anger is mixed with fear because he nearly loses her. He orders that she be removed from the battlefield and sent to safety.

Riftan visits Maxi while she is recovering and finds the copper coin he had given her damaged and blackened. The coin had been a personal talisman for him, and Maxi had carried it with her throughout the campaign. His reaction is unusually harsh because he is still overwhelmed by what almost happened to her. He tells her that Princess Agnes will take her back to Drachium while the remaining forces finish the campaign. Maxi wants to stay, but Riftan refuses. His reaction is not simply anger at her disobedience; he is terrified that she will die if she continues accompanying him.

The coalition finally drives the monsters north. Maxi is taken to Drachium with Princess Agnes and several Remdragon Knights. She is physically exhausted and spends much of the journey sleeping. Her mana depletion cannot simply be cured with magic, so her recovery depends largely on rest, food, and time. Princess Agnes takes responsibility for her care and has healers examine her. Maxi spends days in the princess's residence eating, sleeping, and receiving restorative treatment.

News eventually arrives that the coalition has destroyed the monster army's main camp at the Pamela Plateau. Drachium celebrates the victory, but Maxi remains isolated because she is still too weak to participate in the festivities. She spends her time looking toward the gates and hoping that Riftan will return. She is also increasingly afraid that he has lost his affection for her because she ignored his orders and nearly died. Her fears become worse when she realizes how little she knows about what is happening outside the princess's residence.

The Duke of Croyso arrives in Drachium while Maxi is still recovering. His arrival immediately changes her situation. The duke tells Maxi that she must return with him to Croyso Castle. He is attempting to arrange Rosetta's marriage into the royal family and does not want Maxi remaining in the capital. Maxi initially refuses because she believes Riftan will soon return and take her back to Anatol. Her father then tells her something she did not know: she has miscarried.

Maxi had not known that she was pregnant. The pregnancy had ended during the Livadon campaign, and because she was severely depleted and unconscious, the loss had not been explained to her. The revelation devastates her. She immediately begins blaming herself for the miscarriage, believing that her reckless use of magic and refusal to remain safely at the monastery caused it. She also becomes terrified that Riftan will reject her because she has lost their child. The duke exploits that fear, telling her that a husband will eventually want an heir and implying that Riftan will no longer want a wife who cannot give him one.

Maxi's old insecurities return with force. She remembers her mother's decline and fears that she may suffer the same fate as a woman who cannot provide a male heir. She becomes convinced that Riftan will be disappointed in her. Instead of returning directly to Anatol and facing him, she agrees to return to Croyso Castle with her father. She believes that if Riftan is going to divorce her, it would be easier to face it from her family's estate than from Anatol.

Back at Croyso Castle, Maxi is placed in the same environment she spent years trying to escape; an abusive father. She is effectively confined to the annex where the Croyso women considered undesirable or embarrassing have been kept. Her old nursemaid treats the situation as though Maxi has simply returned to the life she was always meant to have. Rosetta also visits her and cruelly suggests that Riftan may abandon her now that she has miscarried. Maxi defends Riftan, insisting that he is different from their father, but Rosetta points out that if Riftan truly wanted her, he would not have left her in Croyso Castle. Maxi is unable to answer because she is struggling with the same fear herself.

Riftan eventually returns to the capital and learns that Maxi has been taken to Croyso Castle. He goes there with the Remdragon Knights. The Duke refuses to let him see Maxi. Maxi, meanwhile, realizes that Riftan has arrived and sneaks out of the annex in an attempt to see him. She reaches a high terrace and can see the Remdragon Knights outside the castle walls. She spots Riftan immediately. Before she can reach him, one of her father's guards catches her. The duke then confronts her. When Maxi attempts to explain that she wants to see her husband, her father becomes enraged and begins beating her. He strikes her with his cane and grabs her hair, demanding that she speak without stuttering. Maxi is terrified and immediately reverts to the helpless state she experienced throughout her childhood. This time, however, Riftan witnesses the abuse. He enters the room and catches the duke with his hand on Maxi.

Riftan is initially too shocked to understand what he is seeing. He then realizes that the man he has always regarded as a controlling and unpleasant duke has been physically abusing Maxi for years. The duke tries to justify the beating as discipline. Riftan responds by striking him with a chair and then kicking him after he falls. He nearly kills the duke before Elliot and Ursuline restrain him. Riftan's reaction is so violent because he realizes that Maxi's fear, stutter, submissiveness, and constant concern about disappointing him have all been shaped by years of abuse. He even mentions to Maxi that he wasn’t on planning on bringing her away from her home, but now he wants her to never come back if this was what her childhood was like. 

Rosetta secretly helps Riftan and Maxi escape. She has had the guards' food drugged with a sleeping potion and tells Riftan which route to use to leave the castle. She makes it clear that she does not want to be involved officially, but she gives them enough help to get out safely. The Croyso guards attempt to stop the Remdragon Knights at the gate, but they back down when confronted by Riftan and his knights. Riftan declares that Croyso and Anatol are now enemies and takes Maxi with him.

The group travels to Zeno, where Riftan and Maxi spend the night. Riftan personally cleans Maxi's wounds and helps her bathe. Once they are alone, Maxi finally explains how long her father's abuse lasted and why she hid it. She tells Riftan that she was afraid he would discover how inadequate she was and no longer see her as the noblewoman he believed her to be. She believes that the person he loved was an imagined version of her rather than the damaged woman she actually is.

Riftan then reveals that his feelings for Maxi existed long before their marriage. He had noticed her when he was still a young man and had spent years thinking about her from a distance. He explains that she was already important to him before she knew he existed. Maxi's belief that she was worthless therefore contradicts what he has actually felt for her for years. They both cry and finally acknowledge how much fear and insecurity have shaped their relationship. This conversation becomes one of the most important emotional turning points in the volume.

Riftan takes Maxi back to Anatol. The trip is made on horseback because they cannot immediately obtain a suitable carriage, with Maxi riding in front of him on Talon. Once they reach Anatol, Riftan becomes intensely protective of her. He makes sure she eats, rests, and receives treatment. He personally brings her food and monitors her recovery. Maxi notices how much more attentive he is after learning what her father did to her.

The political consequences of Riftan's attack on the Duke of Croyso quickly become apparent. Riftan has formally declared war on the Duchy of Croyso. The Remdragon Knights support him, but the Seven Kingdoms' armistice makes the situation dangerous because nobles cannot simply wage unrestricted private wars. Ruth explains to Maxi that the conflict will likely be resolved through a formal knightly confrontation rather than an unrestricted invasion. The Duke, however, is also preparing a legal attack against Riftan.

The duke petitions for a royal tribunal. His objective is to have Riftan punished for trespassing into Croyso Castle and assaulting him. Because Riftan is a powerful noble and the kingdom's greatest knight, the consequences could include the loss of his knighthood and his estate. The duke begins gathering support among other nobles and royal officials. Hebaron secretly tells Maxi what is happening because Riftan has been deliberately keeping her away from the political conflict. Hebaron also asks whether she would be willing to testify about her father's abuse if the case reaches trial. Maxi agrees because she believes protecting Riftan is worth exposing her childhood trauma.

The royal family attempts to prevent the conflict from becoming a formal trial. King Reuben calls a mediation at Loverne. Riftan, Maxi, the Duke of Croyso, Princess Agnes, and representatives of the king attend. The duke presents the case as an unprovoked attack by Riftan, while Riftan's side argues that he entered the castle to rescue his wife after discovering her father abusing her. Maxi is asked directly to explain what happened.

Maxi tells the king that her father had physically abused her and that Riftan's actions were a response to what he witnessed. The duke attempts to discredit her by claiming that Maxi is weak-minded and incapable of becoming a mage. He also argues that she could not possibly have achieved the magical abilities she claims to possess. This becomes important because Maxi's status as a mage gives her protection under the laws governing the Mage Tower.

Princess Agnes then reveals the solution she has been preparing. The Mage Tower can confirm Maxi's magical abilities, but there is a problem: Maxi has never formally registered as a mage. Her magical training has been conducted outside the Tower's official system. If the duke investigates the matter, he could use that technicality against her and undermine the testimony she has given. The Tower administrators therefore propose that Maxi formally enter Nornui, the World Tower of Wizards, and become an official member.

The proposal is designed to protect both Maxi and Riftan. If Maxi becomes a recognized mage, the Duke will have much less ability to challenge her testimony or use her history against Riftan. The Mage Tower has also agreed to alter her registration date so that her previous lack of official registration will not create the problem the duke could otherwise exploit. Princess Agnes explains that Maxi's magical ability is strong enough that she could potentially complete the necessary training in approximately three years.

Riftan is furious when he learns that Agnes has proposed sending Maxi away. He tells Agnes that if she were a man he would challenge her to a duel. Agnes insists that this is the only realistic way to protect his knighthood and Anatol. Maxi also supports the idea because she believes that becoming a high-ranking mage will solve the legal problem without requiring Riftan to give up his land and title.

Riftan initially refuses completely. He tells Maxi that he will not allow her to leave him again. He has already spent three years separated from her and cannot accept the idea of repeating that experience. Maxi argues that the separation would only last three years and that she could return as a powerful mage capable of protecting herself and helping him. Riftan responds that three years may sound short to her, but he already experienced those three years as an unbearable period of loneliness and longing. He does not want to spend another three years waiting for her.

Riftan even considers giving up Anatol rather than allowing Maxi to leave. He explains that he could surrender his position as lord, take his personal wealth, and find employment under another noble in Livadon, Osiriya, Balto, or Dristan. Maxi refuses to accept this solution. She points out that Riftan has spent years building Anatol and that the Remdragon Knights and the people of the territory depend on him. She believes that abandoning everything he has built simply to avoid being separated from her is not acceptable.

The conflict between them continues after they return from the mediation. Maxi eventually understands that Riftan's refusal is based on his own trauma from their previous separation, while Riftan begins to understand that Maxi's willingness to leave is not because she wants to abandon him. She believes that she must become stronger and more independent. She also wants to ensure that Riftan does not lose his title and home because of her father's actions.

Despite Riftan's objections, the political situation forces the issue. The Duke is prepared to continue the case, while the Mage Tower is prepared to protect Maxi if she joins. The plan becomes the only viable method of preventing Riftan from losing everything. Maxi decides that she will go to Nornui even though she knows the decision will devastate both of them. Riftan is furious at the decision. 

Before she leaves, Maxi continues traveling with Riftan and the knights for a short time. During one journey she becomes separated from the group after an encounter with monsters. Riftan eventually finds her by following her tracks through the wilderness. The encounter reinforces how dangerous Maxi's tendency to separate herself from the group can be, but it also shows how instinctively Riftan searches for her whenever she is in danger.

The final political confrontation occurs when the king, the Duke, Riftan, Maxi, and Princess Agnes meet again. The duke insults Agnes and refuses to accept Maxi's claims. Agnes counters by explaining that the Mage Tower will recognize Maxi as a mage and can investigate the abuse. The duke's position begins to collapse because continuing the case would expose him to the accusation of persecuting a mage. King Reuben then offers him a way to withdraw the case without completely humiliating himself.

The king offers to halve the dowry associated with Rosetta's proposed royal marriage if the duke agrees to drop the matter. If he refuses, the king threatens to cancel the marriage arrangement between the Croyso family and the royal family entirely. The duke finally agrees to withdraw his suit. Riftan keeps his knighthood and estate, and the immediate legal threat against him ends.

Although the trial is prevented, the solution still requires Maxi to enter the Mage Tower. Princess Agnes explains that the Tower has agreed to accept Maxi and protect her from any further attempt by the Duke to challenge her status. Maxi therefore prepares to leave Anatol and travel to Nornui.

Riftan remains devastated by the decision. He argues that Maxi could stay and that he would find another way to deal with the political consequences. Maxi insists that she wants to become a mage and that she does not want him to sacrifice his entire life for her. She also believes that she needs to become capable of standing beside him rather than constantly needing to be protected.

The final preparations are made for Maxi's departure. She packs only the things she believes she will need for life as a mage rather than taking the extensive wardrobe normally associated with her position. The people of Anatol and the Remdragon Knights are aware that she is leaving for an extended period, although the exact length of the separation is expected to be around three years. Maxi knows that the journey to Nornui will change her life completely.

Riftan's anger eventually gives way to desperation. He tells Maxi that he cannot bear another separation after finally having her with him. He is particularly hurt because she made the decision without first trusting him enough to tell him what she was planning. Maxi insists that she is not leaving because she loves him less; she is leaving because she believes it is the only way to protect the life they have built together.

Maxi ultimately boards the ship bound for Nornui. Riftan accompanies her to the docks but does not want to accept the separation. The moment comes when she has to leave him behind and begin the journey to the World Tower. The Remdragon Knights remain with Riftan while Maxi departs for her magical education.