There's no way the demon Incubus is real, it's only in the manga you've read. You are an ordinary student guy who works at a cafe far from the apartment.

Time skip

You wake up startled when you feel your body tingling and running out of energy. You are startled to see a creature lying on your lap, it has horns...tail like a demon..

"Ugh...seems like you've discovered me, but I can't erase your memory if I haven't sucked the energy.." Ji looks at you with his devilish eyes