Seikatsu Shuukan The Animation
Shuntarou is an otaku who completely unashamed of playing or watching erotic titles that have only one theme: love between brother and sister. Naturally, he himself has three sisters who are the cause of his fetish: the busty, easily irritable Ayaka, the beautiful Chiaki and the cynical, flat-chested Fuyuno. When they catch him in his “activities” using their panties, they are hardly surprised, yet all the more disgusted. The next day Shuntarou finds himself mysteriously shrunken. So as not to get caught by his sisters, he introduces himself to them as Shuntarou’s internet friend Koharu and the sisters quickly take a liking to him because of his cute appearance.
Naturally, he takes advantage of this situation in order to get closer to his sisters. Ayaka also doesn’t shy away from anything and immediately makes a move on the little Koharu. Of course, Chiaki and Fuyuno don’t want to miss out either and start throwing themselves at him. Thus the merry game goes around and Shuntarou also learns some of his sisters’ secrets.