Ani-Imo by Haruko Kurumatani

When a freak accident causes Youta to switch bodies with his twin sister, Hikaru, he discovers that his "innocent" sister is anything but, and he becomes the object of Hikaru's romantic advances.

Read the entire series:

  1. Vol. 1
  2. Vol. 2
  3. Vol. 3 
  4. Vol. 4