Dead Mount Death Play

Info:

In a big fight between a hero and a corpse god necromancer, who controls dead bodies, something unusual happens. During the fight, the corpse god necromancer uses reincarnation magic to reincarnate into another world. A boy named Polka Shinoyama is brought back to life in a different time and place. When Polka wakes up, he feels strange and confused because he is not himself.