The moment XX-kun life ended on earth, he was reincarnated as a non-human in a fantasy setting world. Still in this world, human and non-human lived together in harmony. This harmony was shattered by an existence of a "demon emperor." Like any fantasy game goes, the demon emperor was finally defeated by XX-kun and his party... yet, afterward, he was killed... His second reincarnation was into the same world but way into the future.... but, he was reincarnated as a monster being experimented on in a laboratory. One of the experiment went wrong, thus his life ended. The third reincarnation, he again was born as a hybrid monster, half incubus, half ogre in a monster village. Everything seemed to go well until the village was attacked...
Kaga Tada, the protagonist who desperately saved the world after being summoned in another world as a hero to defeat Schnee, the other hero summoned who wanted to destroy the world. Though he did defeat Schnee and saved the world, but he was betrayed by the people he trusted as friends and is stabbed to death by a sword. At that time, he swore: If there is a next time, he would no longer cling to the word called ‘believe’. If there is a next time, he would pay them back as cruelly as possible.