The fantasy story is set in an alternate world where one can choose the form in which one is reincarnated — but choices like the "demon king" or the "hero with cheat skills in a harem" are so popular that one would have to wait in line for one to 50 thousand years. So, our protagonist chooses to be reincarnated over and over again into other bizarre forms, such as the rib of a hero with cheat skills in a harem story's happy ending, a hermit crab, or a vegetable.

[Source: Anime News Network]