Eiken: Eikenbu yori Ai wo Komete

Both are Ecchi OVAs that accurately depict women and human anatomy. 

Both are good comedies. Eiken is a masterpiece. 

Both series feature a poor, put-upon young man (is it a coincidence they LOOK EXACTLY THE SAME??!!) being mentally sexually (in Sakura's case, add physically) abused by a bevy of lovely lolitas. Both of these series are also SICK, SICK, SICK!!! If you're into this type of thing (as I am), you'll love it!! Otherwise, YOU'VE BEEN WARNED!!! 

Don't lie, man. We all know you watch this show for the titties. Well, Eiken delivers boobage too. 

Both are terrible OVAs with fanservice - and a female character who obviously loves the male character. 

What do they both have in common? Sexual undertones, School, Big boobs, shinpantsu, curvy bodies and everything that a guy can imagine, the only differences: One was a 2 episode OVA while the other is a full 10 episode anime  

Both are comedies with a touch of ecchi, though Eiken is way more explicit and Uzaki-chan is more focused on the slice of life comedy. And if you are attracted to cute, colorful girls with very big breasts, maybe you'll like the girls from eiken c: 

Both are ecchi OVAs with a lot of booba. What else would you want? 

MD Geist is to violence what Eiken is to fanservice. Both shows go to the extremes in their respective content, both are OVAs, and both somehow received a second episode (in the case of MD Geist, it's a sequel).  

They are both hentai in nature and have comedy though Rapeman is much funnier.  

Both are series known for the breast-service, but also quite good at butt-service. 

They are practically the same overuse of sexual tropes and fanservice and with no coherent story at all.  

Both anime have panty barrages and often joke around with that sort of thing (subtly or not so subtly), although Eiken is a lot more over the top for obvious reasons, and Najica a fair bit more subtle and handles its main plot a lot more seriously. If you found Eiken genuinely funny and weren't put off by the perverted aspects of the show; I believe you'd find Najica just as great from a comedic viewpoint. 

Weird older OVA where not only the characters have ridiculously huge breasts, but those massive mammaries, those huge milkers, those large knockers, those giant honkerinos are pretty much the main focus of the story.