Several years ago I found a one-shot manga that I liked. Unfortunately I forgot the title, if someone happen to know please inform me!

The story goes like this:
A boy just moved to a new school and having a school trip at a temple with several thousand steps. A girl classmate happen to be an ecchi/hentai mangaka and likes to draw Yaoi stuff. In and unfortunate turn of event, the boy and the girl slipped from the temple stairs and while slipping down, their bodies progressively transform into the other's body (So they swapped chest, crotch, etc). After they reached the middle part of the stairs, they realized that they have switched some of thei body parts. Hoping that continuing to fall down will reverse their change, they do another free fall. At the bottom of the temple stairs, however, they completely swapped body and decided to live on as the other person.

If any of you happen to know this manga, please tell me, many thanks^^