Yamada-kun and the Seven Witches - Manga

One day, high-school boy Yamada bumps into the beautiful girl Shiraishi on the stairs (literally), and their lips touch as they fall. When they regain their wits, they realize that they have swapped bodies. As time progresses, the two realize that this is not the only mysterious happening in the school.
' from ANN
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Notes

Alternative Names: Yamada-kun to 7-nin no Majo
Author: YOSHIKAWA Miki
Artist: YOSHIKAWA Miki
Genre: Comedy, Drama, Ecchi, Gender Bender, Harem, Mystery, Romance, School Life, Supernatural
Demographic: Shounen
Adapted into the anime, Yamada-kun to 7-nin no Majo