Sora no Iro, Mizu no Iro

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. 

While their settings are completely different. Both of the sex scenes from their first episode's sequence are remarkably similar in a good way. While Sora no Iro, Mizu no Iro leads a secret sex life on campus direction, Overflow follows the path of incest. If you loved the high quality animation and artwork of Overflow's first episode, you will find that Sora no Iro, Mizu no Iro is a masterpiece in that regard. 

They both are very tame shows. Both feature multiple girls and 1 guy and they all have consensual sex and no extreme kinky fetishes.  

Awesome hentai animation with simple story! 

They both were drawn by the great Tony Taka!