Reincarnated as a girl, into someone else's harem
Multiple universes have coöperated in an exchange project, called the 'Reincarnation Program'.
A certain young man at the ripe age of seventeen volunteered to live a new life in a world different from his. The exchange is programmed in such a way that the personality of the first volunteer closely resembles that of the second volunteer.
Then again, everybody is unique...