Very soon he saves a beast-girl called Nem (white cat), who idolizes him as master (+1 to team).
Then he will teleport alone to lend the Dragon Heart a hand in destroying the kingdom that summoned him. He kills Aries and Johannes (evil princess and King), but the heroes are not present. He awakens the abyss within himself. Destroys the castle and returns to his companions.
When he returns he realizes that Razhausen (decent kingdom he was staying at) is under invasion. S class monsters out-gun the knights and adventures and it looks bleak. He arrives in the nick of time to save everyone and is seen as a hero. They capture the culprit, who ends up being an asset for "the empire". The city parties and he is acknowledged by the king.
Masamune, Toa, Sierra, and Nem leave for a life of adventure. They pass through a kingdom where a divination expert reveals to Masamune that in the future Toa will die and he will destroy the world. Concerned by this revelation, he charts course to a magic school where he wishes to learn a magic that will prevent Toa's death or be able to revive her. They are admitted and begin classes.
While they go to school Sierra's sister is killed when the empire sends a rescue team to recover their agent. Sierra who is grieving returns to Razhausen and stays there for most of the story (-1 to team). Masamune is then asked by Dragon Heart to take down another corrupt kingdom, which happens to be the kingdom he just passed through. He is less enthusiastic, but serves as support. His abyss power acts up and recoils, causing a little friendly fire. He promises to learn limb regrowth magic and fix his mistake... but never does, and never even tries. He starts to fear his power and what it may do to his loved ones. He also insists on sparing the princess's life, and then he takes responsibility for her (+1 to team).
The choice to learn the magic that revives Toa in the future ultimately gets side-lined and discarded. He helps bind a spirit king to a classmate he grew close to, which happens to be prince of Razhausen. The Spirit king ends up hating him because he brute forced the binding contract to the prince. It's revealed that all spirits are the mortal enemy of the abyss. Then he goes to explore a dungeon. Realizes the dungeon is a manifestation of his abyssal power in the real world and is a domain that's completely comes under his control. He levels up x3 and learns the abyss is "his will", and if he doubts the abyss it will consume him and recoil. He resolves to fully embrace it. Then he returns to school.
I'm gonna super summarize from this point...
Masamune cares for his girls, and his girls love him. As they adventure on, they always run into someone who either wants to kill or covet his women. He delivers retribution every time. Most of the time they are nobles and things escalate. He has mixed public opinion. Some only know him as a hero and and others are exposed to his habit of public displays of extreme brutality and scary abyssal magic. His girls express their concern every time, not out of a sense of justice or anything, but for what his fevers of rage do to his own personality. He ignores their concern.
Masamune kills a few minor heroes secretly and one in a public duel. He comes to regrets how easy and empty revenge is. He then commits to playing the long game of revenge and lets them build a life and develop, just to kill them when they're more happy.
Masamune continues to run into people that trigger his rage all the time, makes chaos wherever he goes. Most people that had a good opinion of him change their mind. A tribunal of kingdoms come to a conclusion. He's a huge risk but he is above their ability to control. They also see him as a potential asset against the empire. They try to rein him in and prevent nobles from messing with him by giving him a nation status and forming treaties. It doesn't really work. Over time he develops a hatred for humans and idolizes all non-humans. Tries to start his own country and I lost interest about there.
Fast-forward to what you really want to know...
Toa dies, her father preserves her body for Masamune to revive, but he never cared enough to prioritize learning revival magic yet. After her death circumstances prevent him from seeking that knowledge.
He kills the princess follower (by accident I assume, I skipped both their deaths).
Sierra contracts with a spirit king. She betrays Masamune by working will other spirit holders to imprison him (cuz he's literally immortal by then). The imprisoning ritual requires all spirit holders to sacrifice their lives. She and Razhausen's prince die. Before he is fully sealed Masamune turns all the spirits kings into demons and they proceed to end the world.
At that point Nem is so distressed by Masamune that she commits suicide right in front of him. He doesn't heal her and finally gets sealed.
Toa's dad gives up hope, stops the preservation magic and buries his daughter.
Ultimately Masamune obtains Abyssal king status and some weird Mantle called "world observer", where he is given the choice to reset the world. He does the reset, and he does it in a way that excludes himself. Then he dissolves into nothing.
The End.
