A guy has sex with his two sisters in the 1st chapter. At the end, you find out he was simply drawing out his desires and his sisters punish him for having such thoughts. His two sisters in the other chapters actually do have sex with him and one of them is tsundere.

Finally found it, Koi Shimai by ryoma.

Ohh, that looks nice. 😉

[img]http://i43.tinypic.com/351e59t.jpg[/img]