Overview:

High schooler Yūta Iridatsu has experienced “astral projection” i.e. his spirit has been separated from his body. He woke up in a mansion named Koraikan and met a cat spirit named Chiranosuke, who told him “You must find the Sacred Tome of Koraikan in order to return to your physical body.” While searching through corridors of Koraikan, Yūta bumped into underpants of its female residents, and doing so would, eh, create some big trouble for planet Earth.