Tsun Tsun Maid wa Ero Ero desu

Both hentai feature purple haired tsunderes as the main love interests over the course of 2 episodes. Both characters show evolving traits as the series moves into the second episode. And of course, both male boys are dense as fuck. I'd defiantly recommend both hentai as they are some of the best in terms of art, story and characters! 

Imouto Paradise 2 is like the better version of Tsun Tsun Maid. Softcore vanilla hentai with cute tsundere girl. 

The main character in "Tsun Tsun" actually has posters of "My Imouto" in his bedroom. They are produced by the same company, have very similar art styles, cater to certain fetishes (little sisters and maids) in similar ways, are both 2 episodes of only 15 minutes long each, and they are both about just one guy and one girl coming together and having sex several times.