Ani-Imo Vol 3

Ani-Imo Vol 3 by Haruko Kurumatani. A Romance manga rated Older Teen, published in English by Yen Press in 2015.

Youta Koizumi has always looked out for his shy sister Hikaru, though the two aren't related by blood. When an accident swaps their bodies, Hikaru reveals a bold side Youta never knew: she has long been in love with him and intends to make him hers. Now Youta has to get through life in his sister's body while the two search for a way to switch back.