Resort Boin

Kanojo x Kanojo x Kanojo and Resort Boin are both really similar OVA series. They both feature a story that follows the male lead an a harem of quirky girls on their daily lives. Both series feature some good animation and art, especially for the characters. Although Kanojo x Kanojo x Kanojo definitely has an edge. Both series have a very calm atmoshpere, occasionally penetrated by humor and general shenanigans. Although I'd say Resort Boin is slightly less comedic. They just have a kind of intrinsic similarity that's hard to put to words. If you enjoyed one of these, then I guarantee you'll like the other. read more 

Both are light-hearted hentai mostly about ultra-busty women competing for one dude's affections. Resort Boin goes into slightly less vanilla territory, but only briefly. 

Both of them are hentai OVAs starting in 2007 with actually pretty competent animation for the time, both are harem with lots of girls and one guy at play too, there's also the fact that there's the student/teacher scenario in both (with the roles reversed), this is definitely more apparent in Kateikyoushi No Oneesan, since Resort Boin is a sequel and they're in a vacation, but they still call him sensei.