Urusei Yatsura S00 E05 Inaba the Dreammaker

"Grab her horns and she might just become your darling!"

It’s summertime and Shinobu happens upon a boy wearing a rabbit costume who drops a key that leads to the room of destiny, a dimension filled with infinite doorways to various possible futures upkeep by a group of sentient rabbits. Together with the bunny boy named Inaba, Shinobu, Lum, and Ataru seek happy futures for themselves.