Akiyama, who died in his original world, was assigned to the body of an original resident of another world.
It seems that in order to change his past self, Lingqiu chose to hand over his soul to the devil in desperation. In this way, his body will usher in a new owner, which is Akiyama's soul. All this changed from this moment on. The originally cowardly boy suddenly underwent earth-shaking changes, making others wonder whether he had been hiding his strength in the past and whether he had any terrible thoughts.
I still don't understand how Akiyama died.