Light Novel Volume 17/Synopsis

Prologue: The Coronation
In the aftermath of the Takt's invasion of Melromarc, the world started to rebuild. Faubrey and Shieldfreeden who backed Takt are now paying for repairs and defense against the waves. Due to Queen Mirellia Melromarc's death, Trash coronates Melty as the popular new queen. After the ceremony, Naofumi's party congratulates Melty and Naofumi teases her about her new responsibility. In response, Melty retaliates and makes him an archduke. Upon hearing this, Trash proudly approves and reminds them that as an archduke, the two of them are technically engaged. Both Naofumi and Melty try to refuse but their pleas land on deaf ears and their engagement remains.

Chapter One: Talk of Love
After the ceremony, Naofumi heads back to his village and meets Ren and Eclair. Naofumi and Ren discuss what they want to do when they defeat the waves. Ren still hasn't decided whether he wants to stay or go back to his world since he's now made valuable relationships - including with Eclair. However, Eclair seems oblivious to his affections and doesn't seem to be ready for a romantic relationship. Naofumi encourages Ren while Ren and Eclair teleport to the Melromarc's castle.

Chapter Two: Limit Break
Heading further into the village, Naofumi meets up with Ethnobalt who had recently crossed over from his world. According to Ethnobalt, they have three days before they can cross over again so Naofumi plans to level up and prepare. The first thing on his agenda is to use Gaelion's new knowledge as Dragon Emperor to break the level-100 limit for their party. Everyone who was ready, including Sadeena, Shildina, Raph-chan, and Raph-chan II, got the level breaking ceremony. After the ceremony, Naofumi went training in the ocean with Sadeena, Shildina, Ruft, Raph-chan II, and Ethnobalt. The two killer whale sisters show a massive improvement in abilities while Ruft reaches the level 40 limit. Back on land, Ruft receives a special class-up from Raph-chan and is sent to learn leadership with Melty. Using the experience-rich seabed, Naofumi and Ethnobalt train the remaining 3 days until Ethnobalt reaches about level 100 and Naofumi reaches level 150. Finally, Naofumi heads over to Erhard's shop to upgrade his equipment to be compatible with Ethnobalt's world.

Chapter Three: Party Selection
The day before Naofumi leaves to Ethnobalt's world, he and the other Legendary Heroes meet up to discuss who should be on the rescue party. According to the shield, he can bring multiple people along but are limited by the number of legendary heroes. Filo and Rishia were selected since they previously went to that world and their levels would only be reset to what they were over there. Itsuki, S'yne, and Raph-chan volunteer and are accepted into the party. Sadeena is allowed to come while her sister was eventually convinced to stay to protect the village. The rest plan to stay at the village.

The next morning, the party prepare to head out. When everyone was ready, Ethnobalt used his accessory to travel to his own world.

Chapter Four: Arrival into Conflict
Upon reaching Ethnobalt's world, Naofumi discovers that Shildina was accidentally caught up with them during the transit. As expected with moving to a different world, everyone who hasn't been to Ethnobalt's world was reset to level 1. As an unexpected result, Shildina transformed to a child.

Looking at their surroundings, they find that they are near L'Arc's castle. Traveling to the castle, Naofumi's party finds the area in chaos. Raphtalia and L'Arc's party are being driven back by an unknown enemy force who was using L'Arc's Vassal Scythe. With seemingly no option left, Glass prepares to use the curse series of her Vassal Fan. As he arrives, Naofumi stops her and casts his most powerful buff spell on his allies. With their new strength and backup, the enemy is quickly defeated and the Vassal Scythe is returned to L'Arc. Raph-chan destroys the soul of the leader of the enemy to prevent him from reincarnating.

With most of the remaining enemy retreating, Naofumi finally reunites with Raphtalia. He updates Raphtalia and this world's heroes on what happened with Takt's invasion. After the joyful reunion, Naofumi introduces the new people from his world and L'Arc updates them on the latest events. After Naofumi had last visited her world, Kizuna tried to summon the other Legendary Heroes for help with the waves. They refused, believing that they were just in a video game, and were eventually killed by a group of Vassal Weapon wielders. Kizuna tried to hold a meeting to stop and punish these vassal weapon holders but someone she thought was an ally attacked. She was captured and L'Arc's scythe was stolen. After recounting recent events, L'Arc and Naofumi decide to rescue Kizuna together.

Chapter Five: Inter-World Adaptation
Preparing to save Kizuna, the members of Naofumi's party who were reset to level 1 were given earth crystals to level up. In the meantime, Naofumi and the heroes from this world went to meet Romina the blacksmith. Naofumi asks her to tweak his current Barbarian Armor to be fully compatible for this world. He also returned the Demon Dragon core which had previously possessed Gaelion. Finally, he requested weapons for the rest of his party since some of their equipment stopped working after changing worlds. Romina accepts and on the side mentions that L'Arc is jealous of Naofumi since Therese adores his accessory crafting skills.

Chapter Six: Hidden Abilities
Returning to L'Arc and his party members, he found that Sadeena and Shildina have significantly leveled up and are now training with L'Arc. Eventually, L'Arc is challenged to a drinking contest with the two killer whale sisters which he hastily agrees to try to make Naofumi feel jealous. Therese tries to get him to back down but he insists on the competition. After everyone eats a meal that Naofumi had prepared, the three start the contest. L'Arc almost immediately gets drunk and collapses.

After the meal, while Naofumi is talking to Glass about the worsening waves, Itsuki starts to play music with the band. He shows extreme talent for an instrument that he hadn't played before and even starts to conjure magic with his music. Naofumi then talks to Shildina and Glass and discovers that spirit people are innately afraid of Shildina due to her oracle powers. Afterwards, Glass and those in Naofumi's party with a sufficient level go out to look for Kizuna.

Chapter Seven: Finding Kizuna
Naofumi, Glass, Raphtalia, and the two shikigami travel by carriage to look for Kizuna. Both Raphtalia and Glass scold Naofumi for being reckless with Raph-chan. During the next few days of looking, Naofumi also creates an accessory for Chris.

Back at L'Arc's castle, the heroes review the status of the legendary and vassal heroes of this world. They believe that the Vassal Musical Instrument hero may have kidnapped Kizuna but his country is feigning ignorance. Thankfully Naofumi's party has been doing extremely well leveling up so they are now all ready to rescue Kizuna. Immediately after Chris located Kizuna, the Vassal Mirror surprisingly appeared and helped teleport the group to nearby the marked location. After initial reconnaissance, the rescue group headed to a nearby town.

Chapter Eight: Subterranean Maze City
At the outskirts of the town, the rescue group prepare their disguises for infiltration. Raphtalia plan uses magic to disguise herself while Sadeena and Shildina buy fake jewel cores to pretend they were part of the jewel race. With their preparations complete, they follow Chris out of town to rescue Kizuna.

Two days later, they reach an unknown castle. Naofumi plans to find Kizuna's prison while L'Arc and Sadeena plan to locate the dragon hourglass. The others scout the capital city. Before splitting up, Ethnobalt and Glass mention that the town was built on top of an underground maze. After splitting up, Naofumi and Chris find that Kizuna is likely getting held in this maze and they cannot search any further without being conspicuous. They then go to a rendezvous to catch up with the other two groups.

The other two reconnaissance groups were successful in finding information. They found that the dragon hourglass was heavily guarded and being experimented on. They also found a partial map of the maze and information on the suspicious Vassal Musical Instrument wielder - Hidemasa Miyaji. With the sun setting, they figure out their rescue plan.

Chapter Nine: Outsider Theory
As soon as it got dark out, the rescue part split up into three groups. While L'Arc and a few others caused a distraction at the dragon hourglass, those who can be stealthy snuck into the underground prison. Naofumi, and a few others acted as backup in case anything went wrong. After a few minutes, Naofumi and his group also headed into the underground maze with Raph-chan guiding them. After passing through a teleportation trap, his group is split up and he, Itsuki, Glass and Raphtalia are confronted together by the Vassal Musical instrument user, Miyaji. Miyaji pretends to know nothing about Kizuna's captures and tells them to go home. However Naofumi is insistent and eventually pries a confession out of Miyaji.

Just as the two groups prepare to fight, Naofumi and Itsuki's stats and abilities from being Legendary Heroes were suddenly suppressed. Apparently, Miyaji had successfully experimented with a dragon hourglass to remove the authority of Legendary Weapons from other worlds. S'yne teleports in to their defense and mentions that L'Arc's group was successful in their escape. As the heroes are severely weakened, Malty appears and praises Miyaji for "defeating" Naofumi.

Chapter Ten: A Familiar Face
Miyaji thanks Malty for her help in capturing Naofumi and Itsuki. Along with with Malty, Mald appears with the Vassal Axe and his own twisted sense of "justice". He is intent on killing the Legendary Heroes of Raphtalia's world and has aligned himself with the vanguards of the waves. Finally, another newcomer appears alongside Miyaji. This evil woman with a corrupted vassal chain introduces herself as S'yne's sister. Apparently she provided the information used to suppress Naofumi and Ituski's Legendary Weapons. After a slight squabble between the vanguards of the waves, the fight against the heroes begin.

Raphtalia and Glass took on the hardest of the fighting since they still had their Vassal Weapons. In the back, Naofumi used Hengen Muso and Way of the Dragon Vein to fight and Itsuki used music magic. Eventually, Miyaji was able to cripple Glass and Raphtalia while Mald attempted to kill Naofumi with a cursed series weapon. At the last moment, two balls of light appeared in front of Naofumi.

Chapter Eleven: The Mirror Vassal Weapon
The two balls of light flew underneath and stopped Mald's cursed attack. Naofumi could just barely make out that the balls of light were the Vassal Book and Vassal Mirror helping them out. After saving Naofumi from the attack, the Vassal Mirror flew into Naofumi while the Vassal Book flew away. Realizing that the Vassal Mirror chose him as its new wielder, he tests his new skills against Mald. While Naofumi fought Mald, Itsuki started using music magic to interfere with Miyaji using the Vassal Musical Instrument. As Miyaji prepared to use a cursed skill, Naofumi summons Raph-chan and Chris. The two shikigami reflects Miyaji's attacks and frees Glass and Raphtalia from his previous attack. Raphtalia teaches Naofumi about the various power-up methods from Glass' world which he then applies to his mirror. Finally, Naofumi and his party start to successfully push back against the vanguards of the waves.

Chapter Twelve: A Falling Out
With Naofumi's help, Glass runs out of the room to look for Kizuna. Miyaji continues to buff and defend his group while Mald recklessly attacks with his cursed weapon. However, Mald keeps on hitting Miyaji's harem with his wild attacks which causes the two to start to bicker. Just when Mald was about to hit Naofumi with a devastating hit, Rishia arrives and distracts him. Apparently the Vassal Book had left to lead her to this room.

With the opportunity to finally repay the damage that Mald had caused to herself and Itsuki, she challenges him. She proves that she is not the weakling Mald thinks so is as she expertly starts to overwhelm him. During the fight, Itsuki continues to interfere with Miyaji and both of the Legendary Heroes notice the accessory on the Vassal Musical Instrument. S'yne's sister reveals that if the accessory is destroyed, the weapon will leave for a more suited wielder. Realizing that they are starting to lose ground, the vanguards of the wake redouble their bickering until Miyaji merges with one of his spirit women. Suddenly, lightning struck all around him.

Chapter Thirteen: Forced Possession
As Miyaji was getting struck with lightning, Shildina appeared from the corridor Glass had escaped to. She was using her oracle powers force one of Miyaji's spirit women to empower her similar to how Miyaji was getting empowered. Behind her was Ethnobalt as the new Vassal Book wielder. With his new weapon and the Hengen Muso training from Raphtalia's world, he was able to attack Miyaji and remove the accessory controlling the Vassal Musical Instrument. The Vassal Musical Instrument then flew to Itsuki as its new owner. With his main weapon gone, Miyaji tried to wrestle the Vassal Axe from Mald who immediately cut him in half. In retaliation, Mald also destroyed Miyaji's soul to prevent him from reincarnating. With Miyaji dead, his harem then asked to S'yne's sister to be their new leader.

Chapter Fourteen: Quick Adaptation
After having her fun "playing", or fighting, with S'yne, S'yne's sister finally turns her attention to the other heroes. Assessing the situation, she gives an update to an unknown entity and then casually decides to leave. Before anyone can stop her, Mald barges in and attacks Itsuki. Showing his proficiency in his new weapon, Itsuki easily subdues Mald. Malty then takes the Vassal Axe from him and tries to attack as well but Naofumi easily reflects her attacks. Begrudgingly, S'yne's sister takes the two villains to prepare to go. However, before she leaves, She warns Naofumi to not be too confident in his abilities. She also reveals that she is part of the organization who sent the other-worlders to attack as "low-level thugs." She then vanishes.

Immediately after S'yne's sister leaves, Sadeena, Glass, L'Arc and Therese arrive. They apparently were successful in saving Kizuna and capturing the dragon hourglass.

Chapter Fifteen: Mirror
After the battle, L'Arc and Itsuki confront the Vassal Musical Instrument nation about their hostile action. With the previous user being a fake and Itsuki being the current wielder, the nation steps down. Glass shows Naofumi the petrified Kizuna. They teleport her back to L'Arc's country and believe that she can be cured in about 2 days. They then discuss the path forward. Since the Vassal Musical Instrument nation has been stopped, the Vassal Harpoon is the next largest enemy force.

After the discussion, Naofumi prepares a meal for everyone and reveals that the mirror's power-up method is by eating high-quality food. He continues to stuff everyone with food until they reached their limit.

Epilogue: A Responsibility to Justice
After the meal, when most people had gone to bed, Naofumi came across Itsuki looking into the night. Itsuki then confesses that he has recently been pretending that he was still under the curse that suppressed his personality. Apparently, he didn't have the pride to admit that Naofumi is doing the right thing. Itsuki praises Naofumi for how he has been raising the village and training them to take care of themselves. Itsuki mentions how he had hurt Rishia by rejecting her but Naofumi encourages him. Itsuki then reveals that when the waves are over he wants to travel this world to help people. Naofumi notes that Itsuki has matured. Both then decide to get some rest.