Ani-Imo Vol. 1 (manga)

See?

In this body, I can do whatever I like to “my sister.”

Youta has always had a soft spot for his twin sister, Hikaru. Soft spoken and docile, she’s everything a doting big brother could hope for! But when a freak accident results in the siblings swapping bodies, Youta discovers that his “innocent” little sister is anything but!

Now trapped in Hikaru’s body, Youta becomes the object of his “little sister’s” advances–advances she now has the testosterone fueled power to back up! Will Youta ever get his body back in this uproarious forbidden love comedy?