This is the R18 version which includes adult sex scenes! Based on Hato Konro's slapstick adult manga.
Aikawa Sousuke is an part-time worker who lives in a run-down apartment. One day he hears a creaking sound from his ceiling, and suddenly the resident of the apartment above his, Unyuu Sunao, falls through a hole that appears in his ceiling onto his bed. Thus starts Sousuke and Sunao's comical life of living together.