Fault!!

Both series tell stories of girls who feel in love with the same boy. Each animation : Sora no Iro, Mizu no Iro (swimming) and Fault!! (tennis) use some discipline of sport as a background for their stories. They are "must-see" for Tony Taka's art fans and not only as both series stand out when it comes of character design and animation. 

I found both hentai's having a similar feel to them in the way of character development even though there polar opposites when it come to there stories.  

Both anime about love between siblings Only if you like romance between mio & Shuuichi  

both are involving tennis club, 2 heroine and 1 mc in the beginning 

Similar character designs. Another great by the famed artist Tony Taka.  

-Both anime has the same Incest. But Fault! is more extreme (you could consider this anime as hentai) -Both anime has the sister and brother love (sex)