Joshi Ochi!: 2-kai kara Ero Musume ga Futte kite, Ore no Are ni!?

Sosuke Aikawa lives in a run-down apartment. One night, the ceiling caves in, and the upstairs tenant falls on top of him...
Notes:
• Originally serialized as a web manga under the title Onnanoko ga Ochita Saki wa, Ore no Musuko no Sakippo deshita. (女の子が落ちた先は、俺の息子の先っぽでした。).
• Simultaneously released in long-strip and traditional formats, with 72 episodes and 24 chapters respectively.