Light Novel Volume 9/Synopsis

Prologue: The Waves of Another World
Naofumi fought in a Wave together with Kizuna's friends, successfully fend it off, and evacuate the village where it happened. After the Wave, Naofumi reminds them that his mission in this world is to punish Kyo and bring the Spirit Tortoise's stolen energy back to his world.

Chapter 1: Otherworldly Techniques
Naofumi met Altorese, a friend of Kizuna. Alto whine about how the recently summoned heroes, vassal weapon holders, and other countries in their world seem to underestimate the threat of the waves. Altorese showed an ancient book to Kizuna that depicted cooperation between worlds. They then discussed Kyo, the state of his expanding home country, and an inevitable war with them.

Chapter 2: Quick Draw
Naofumi went to the castle's training ground to hand over Raphtalia's sheath. Glass confirmed that despite having low prana, Rishia indeed has the talent to get stronger. Ethnobalt revealed to have stats growth similar to Rishia's, and then Naofumi motivates him to work hard as Rishia did. Naofumi handed Raphtalia's sheath which gave her a haste-like ability and handed Altorese's book to Rishia for her to get some information from it. When he got Spirit Tortoise Heart Shield, Naofumi unlocked a technique similar to Therese's gem magic, so he asked Therese to teach him magic in order to learn how to use the technique.

Chapter 3: Lure
The next day, Naofumi and co. went to Ethnobalt's hometown. Based on what Ethnobald said, his race is likely to be the parallel version of Filolials. The party took off to their original destination, a labyrinth for leveling up to prepare for the coming battle with Kyo. The following day, after the leveling, the party went back to the castle to resume Raphtalia and Naofumi's sword and magic training. Filo unlocked two fowl forms from previous level-ups and gained an ability to sing which seems to affect Raphtalia and Naofumi's performance. Done with the training, they went to sleep.

Chapter 4: Like a Charging Wild Boar
In the middle of the night, Naofumi and co. awoken by the sound of an explosion. Downstairs, a girl named Yomogi enters Kizuna's house, claiming to come on behalf of Kyo to punish vassal and holy weapon holders. She uses a strange sword made by Kyo and proven to be a quite formidable opponent. After a prolonged fight, Rishia disarmed Yomogi with an ofuda, but something like a vine shot from the sword and wrapped itself around Yomogi's arm and took control of Yomogi's body. Kizuna used her ability and successfully helped Yomogi drop the sword. Naofumi and Glass then careened the sword out of the house before it exploded. Rendered harmless without a weapon, Naofumi captured Yomogi.

Chapter 5: Together, With Conditions
Reinforcements from the castle arrived and asked for assistance at the castle where L'Arc is currently having trouble dealing with the enemy's ambush. Yomogi, unable to believe that Kyo is behind all these attacks, asked Naofumi to bring her along to witness it with her own eyes, in exchange for information about Kyo. Naofumi brought Yomogi along but kept her under a control ofuda to prevent treachery. In order to prevent the enemy from having a strategic advantage, Naofumi went to secure the Dragon Hourglass first. Glass stays behind to guard the Hourglass, and the rest of the group proceed to the castle to help L'Arc and Therese. The enemies attacking the castle revealed to be the group of Trash #2's cohorts which have been enhanced by Kyo with holy beasts' clones power. Yomogi still didn't believe all these is Kyo's doing, decided to help Raphtalia fending the enemies off. The enemy leader is getting serious and started to use a spear with a similar look to Yomogi's exploded weapon.

Chapter 6: The Reformed
Tsugumi, the enemy leader, gets even fiercer by using the spear. Naofumi switched to Shield of Wrath and managed to burn the enemies. Despite the severe damage, the enemies seem to be able to regenerate and went berserk. When the spear is about to explode, Kizuna managed to disarm Tsugumi and Naofumi absorb it with his shield. Resuming the fight, Kizuna used her skill to vanquish the enemies' beasts enhancement. Realizing that they are being used, the enemies surrendered, revealed that they have a third parallel assault at the Hourglass, and decided to warn their fellows about Kyo. Naofumi and co. went to the Hourglass to help Glass and once again subdued the enemies. The subdued enemies revealed that Kyo planned to use the Hourglass to teleport as many troops as he wanted.

Chapter 7: Barbaroi Armor
As promised, Yomogi told Naofumi and co. what she knew about Kyo and pointed out his headquarters location. The equipment that Naofumi ordered are done and he divvied it up to Raphtalia, Filo, and Rishia.

Chapter 8: Two Swords
Preparations for the battle is done and it is time to depart. After days of travel using the vassal boat, Naofumi, and co. arrived at the area where Kyo's secret laboratory is located. Despite trouble caused by mist set by Kyo as a defensive measure in the area, Raphtalia and Raph-chan's affinity to illusion magic enabled the party to find the lab.

Chapter 9: Kyo's Laboratory
Holy beast-enhanced guards appeared at the courtyard. This time, the enhancement is more aggressive and the hosts barely have control of their body. Ethnobalt and Chris, exploiting the enemies' berserk nature, stays to keep them distracted while the rest of the party proceed toward the mansion. The mansion's interior also guarded by another beast-enhanced guard. The group works for Kyo in hope that their ally, Albert the mirror vassal holder who has been taken as hostage by Kyo, can be saved. Incapacitated most of the guards, Naofumi, and co. proceed to enter the underground laboratory and found some homunculus in glass tanks including the mirror vassal holder. Most of the homunculi then opened their eyes, turned into the four holy beasts, and attacked. Kyo then appeared with an army of Spirit Tortoise Familiars.

Chapter 10: When Trust is Lost
Found out about the truth about Kyo, Yomogi resolved to take him down. Rishia entered her awakened state for the fight. Kyo used powerful gravity magic to restrain everyone but Naofumi used a new counterattack skill to temporarily break the magic. Kyo then used magic that worked on base stats, effectively damaged everyone bar Rishia who have low stats. Supported by Naofumi and Kizuna, Rishia attacks but Kyo used Albert as a meat shield. Kyo then used more of Spirit Tortoise energy but a lot of it flowed to Naofumi's shield, once again enabled the access to Spirit Tortoise Heart Shield. Gained a skill to control gravity from the Heart Shield, Naofumi disabled the magic. After a prolonged tug of war, Kyo used magic to summon a Wave, automatically separate Naofumi and Kizuna's party.

Chapter 11: Sacrifice Aura
Due to the Wave's temporary intersection between worlds, Naofumi, and co. regain their original levels and abilities. Rishia gets an even stronger boost, dominating the fight. Kyo used magic that transforms the surrounding into a different place, filled with a barrage of deadly attacks. Naofumi ordered Raph-chan to use illusion magic that proven to be quite effective to disrupt Kyo's attacks. Found a chance to counter Kyo's magic, Naofumi decided to use Shield of Wrath and successfully dispel the magic. Kyo used an attack resembles the head of Spirit Tortoise, and in the desperate time, Naofumi casts All Sacrifice Aura on Filo.

Chapter 12: A Heavy Price to Pay
Empowered by All Sacrifice Aura; Raphtalia, Filo, and Rishia managed to break through Kyo's defenses and wound him. Naofumi destroyed the Spirit Tortoise Kyo cast before, canceled the attack. Naofumi grabbed the defenseless Kyo so the rest of his party can attack him unhindered. Naofumi used Iron Maiden to finish Kyo off but failed. Left barely alive, Kyo activated his cursed series and used a deadly skill. At the same time, Ost appeared and enabled Spirit Tortoise Heart's Energy Blast. The two skills collided and ensured a power struggle. With the help of his party and Vassal Mirror, Naofumi won the struggle and Rishia's attack delivered a fatal blow to Kyo, killed him a moment later. Kyo's Vassal Book then rose into the air and summoned a body containing Spirit Tortoise's energy. Kyo's soul appeared from the book and tried to join the body. Prepared for the possibility, Naofumi ordered Rishia and Raphtalia to use Soul Devourer ofuda and Spirit Blade to finish Kyo off. With Kyo's soul dispersed for good, Naofumi ordered the party to destroy everything in the laboratory.

Epilogue: Kizuna Between Worlds
Spirit Tortoise's energy absorbed to Naofumi's shield for repatriation. All Sacrifice Aura revealed to have stats penalty across Naofumi's party. The Vassal Book and Vassal Mirror Weapons guided the weakened party to get out of the lab safely. The Vassal Mirror Weapon also teleported Kizuna's party to escort Naofumi. Everyone is back to the castle with the Vassal Ship and L'Arc held a victory party. On the day of departure, Naofumi and his party spend their time talking and exchanging gifts with Kizuna, Glass, L'Arc, Therese, Ethnobalt, Altorese, Romina, Yomogi, and Tsugumi. Vassal Katana seems to decide to stick with Raphtalia despite the latter's willingness to let it go. After Kizuna and her party expressed their gratitude, Naofumi, Raphtalia, Filo, Rishia, and Raph-chan teleported back to the previous world.