Light Novel Volume 21/Synopsis

Prologue: Use of Floating Weapons
After celebrating the victory against Piensa, Ren asks to train with Naofumi. However, this time Naofumi was asked to fight with floating shields as if they were swords. Apparently Ren's earnest training has made some progress as he was easily able to take on multiple floating weapons. During the duel, Eclair, Raphtalia, and Fohl observe and make comments on Naofumi's fighting style. In the end, Ren lost the duel due to his tunnel vision. Ren then reveals that he asked Naofumi to fight that way to emulate a powerful opponent from a game he played in the past. However, it seems to Naofumi that Ren has created his own version of the most powerful enemy in part of his motivation to get stronger. After some musing, Ren returns to blacksmith and Naofumi heads to Siltran.

Chapter One: The Siltran Situation
As Naofumi walks through Siltran, he spots Keel and the residents of Lurolona Village helping out and trading with the Siltran people. Even the children protected by the ancient hero Mamoru were helping out. Entering the castle courtyard he finds S'yne making progress learning how to sprout energy wings from R'yne. He is then directed to Mamoru who is already in a meeting with Melty and Ruft.

Entering the meting, Naofumi is debriefed on the political situation. Their victory against the mighty Piensa had made the small nation of Siltran seem like a mighty force. While other nations are now hesitant to attack Siltran, it seems like Piensa is trying to ruin Siltran's reputation. Now that Naofumi was seen in the battle against Piensa, it is also useless to keep his identity as a Hero hidden. Finally, they discuss the Bow Hero and hypothesize that Piensa is using someone he cares about to keep the hero on their side. After the meeting, Naofumi went back to the town to help Keel and the others with their work.

Chapter Two: Wagon Travel with Keel and the Gang
After a successful time trading in Siltran, Naofumi decides to move to begin trading outside of the Siltran castle town. After Keel teases Naofumi about his relationship with Raphtalia, Naofumi decides to bring her on the trip, along with Cian, Raph-chan, and Imiya. While Chick is pulling the cart, Naofumi bonds with the other children - teasing Keel and getting the know the usually guarded Cian. Eventually, they are able to make it to the remote village where they were able to trade and gather materials. As the party are hunting monsters, they are suddenly attacked by a wave of deadly creatures. The party seemed able to hold them off, but once a two-headed monster like the Cerberus appeared, Keel started to panic and the group retreated.

Chapter Three: Wave Trauma
After retreating to safety, Naofumi tries to determine why Keel went berserk. It seems that Keel, and likely other village children, have leftover trauma from the first wave. Any multi-headed monster might remind them of when their village was originally destroyed. Realizing that this might be a wide-spread issue, Naofumi decides that he needs to help the village children heal from the trauma. Returning to the village, he confirms his suspicions that it is a widespread problem and consults Rat for therapy options. In the end, the affected villagers decide to undergo dream therapy.

After figuring out a path forward, Naofumi goes to Raphtalia to stroke her head (after explaining and getting permission). Later on, Raphtalia gives him permission to stroke her tail.

Chapter Four: Thanks to the Assassin
A few days later, Mamoru arrives in the village. Apparently, they were able to find the pacifier from Q'ten Lo which seems to be one of Raphtalia's ancestors. After a few preparations, they teleport to a neighboring nation where they find her over a recently killed fox-demon like Tulina. After the accompanying Water Dragon killed the corrupted king, the heroes and pacifier flee the nation.

After catching a breath, the two groups introduce themselves. The ancient pacifier introduces herself as Natalia. Unfortunately neither Natalia nor the Water Dragon know anything about to get back to the modern-day. After a brief conversation, the pacifier and her dragon decide to inspect Lurolona Village.

Chapter Five: Genetic Modification
As the group head towards Lurolona Village, they talk about the role of the Heavenly Emperor of Q'ten Lo and the sealed monsters they have put away. They give Natalia and the Water Dragon a tour of the village and as they do so they learn that Keel has gone missing. Arriving at Rat's lab, they learn that Holn may be responsible for Keel's disappearance so they enter inside. As they travel further, they notice that Holn has made several changes to the lab, including a secret basement lab.

Suddenly, the ground shakes. As the group heads back outside, they notice several towers growing out of the ground. In order to unlock the lab, someone has to climb on top of each of the seven towers.

Chapter Six: Mikey
At the front of the lab a barrier prevented anyone from entering. After teamwork and significant effort from Natalia and the Water Dragon, a small force is able to pass through. As they travel through the new addition, they find several interesting experiments including a humongous Raph duplicate made of slime. After some fighting it is revealed that the Raph duplicate is Rat's beloved monster Mikey. At a critical moment of decision between saving Mikey or Keel, Naofumi asks to speak with Keel before she makes a decision. Surprisingly, Holn accepts and allows them through.

Chapter Seven: The Raph Species Upgrade Plan
Naofumi and his party continue into the lab as they hypothesize what type of research Holn is conducting. They find Holn who then points them towards Keel. As they try to talk down Keel from being "modified", she reveals that while the therapy is working, it's not actually improving her current condition. To that end, she wants to get stronger so she has no reason to be scared. Talking to Holn, she describes her ability with the Vassal Whip to bring forth latent potential from a person's potential. In Demi-Humans like Keel, it can unlock the second transformation called Beast Transformation. Holn then decides to give Keel a "trial run" of different possible "upgrades" through illusion magic. However, in the end, since Keel would be unable to revert the beast transformation everyone decided to indefinitely postpone the operation. Holn then gives Naofumi a rare material which was used to unlock several shields. After Holn reverses the transformations done in the village, Natalia chastises her and the Vassal Whip spirit.

Chapter Eight: The Troubles of the Shield Hero
After the incident with Holn, the village settled down for a few days. Seeing his efforts to help the villagers overcome their trauma, Cian asks Naofumi to help "save" Mamoru. She then asks him to covertly rendezvous at Siltran castle during nighttime so she could show him something. Upon arriving, Cian guides Naofumi and his small party into a hidden base past several traps and security devices. Inside, they find Mamoru in the process of experimenting with demi-human children to make the stronger. It seems that Mamoru is responsible for creating the four elite races of Siltvelt. Upon revealing their presence, Naofumi's party is attacked by Mamoru and his children.

Chapter Nine: Confusion Target
As Naofumi's small party fights against Mamoru's, it seems that they are evenly matched - shield hero against shield hero. The fight wages on and Mamoru displays some powerful moves. However, over time, Mamoru's team pleads for him to stop and reconsider. Eventually, Cian and R'yne get to him and the fighting stops. Mamoru then asks for forgiveness from his allies. It strike that unlike the women who easily forsaken the vanguards of the waves, Mamoru's children fully believe in him and ask Naofumi to forgive him. Mamoru then explains that he is doing all for his recently deceased beloved Filolia. He wants to get stronger so that kind of death would never happen again. At the same time, he is also trying to revive her from death. At this point, the emotional toll starts to become too much and Mamoru breaks down crying.

Chapter Ten: Filolia
In front of Filolia's cultivation tank, Mamoru explains how he was able to "save" her soul and is trying to revive her. Naofumi then realizes that these experiments are the source of the filolial race. To Mamoru and Holn's surprise, Raph-chan shows off her strong spiritual powers and offers to help with the revival. After a long night's work, Raph-chan successfully extract's Filolia's soul from the Suzaku fragment and they transfer the soul into the homunculus body. The Vassal Claw also shows up to provide help. However, just as they finish, they receive warning that another wave will occur within an hour.

Chapter Eleven: The Imitations (Improved)
Heading to the village, everyone prepares for the oncoming wave. The most impressive development is that Holn was able to modify the Legendary Weapon Replica so that anyone could use them (albeit at a greatly reduced power output).

Chapter Twelve: The Origin of the Waves
As the countdown reaches zero, the waves begin. However, these are unlike any wave Naofumi had seen before. Unlike the horde of monsters he was used to, person acting like a game show host appeared. He teleported the ancient Bow Hero to fight against a Legendary Hero. of another world. At the same time, he created a maze of oncoming monsters for everyone else to fight. It turns out that these waves of the ancient past are a form of entertainment for the "godworld" - a world of technologically advanced people who are essentially immortal. Hearing that these are the people responsible for the waves, Ren attacks the host but is immediately stopped by the self-proclaimed god's overwhelming power. The host announces a fight between himself and Naofumi with all modern-day weapon users.

Chapter Thirteen: How to Kill a God
As the battle begins, it becomes clear that "Cathead", the host of the show, is more than they can take on. He sends Raphtalia flying in one hit and can break through Naofumi's shields with ease. Suddenly, everyone's weapons pulse and show their 0 series. Remembering that this had been effective against the waves earlier and that it is "highly effective against those to possess eternity", they switch to it in a surprise attack. Unlike earlier, Naofumi is able to reflect all attacks with ease. They are able to destroy both body and soul of the self-proclaimed god. With the enemy's defeat, the waves start to recede.

Epilogue: The Fear of Those Who are Eternal
The rest of their allies are able to wipe out the remaining monsters from the wave. The heroes then briefly celebrate. Then they were approached by another self-proclaimed god nicknamed "Doghead". The self-proclaimed god threatens them and it becomes clear that the entire enemy world has now been stirred knowing that they can be killed by the worlds they were playing with. The enemy run aways while Naofumi and the others start to discuss the 0 series. They then clean up and return to Siltran.