Koi Koi 7

6 girls plus ecchi plus two minor female characters who are in love with each other, koi koi 7 has Isuzu Yamada and Subaru Satou while girls high has nao koshiba and sayaka mouri, and the heroines are all students of an all-female school 

6 girls and one guy, though lamune is the dramatic version while koi koi 7 is the comedy version.. plus both series have a tomboyish and tough girls:Hikari Nakazato and Sakuya Kazamatsuri, and pink haired girls yayoi asuka and misora ayukawa 

both series' protagonists wears glasses and are romantically linked to their pink haired heroines plus in koi koi 7, the heroines led by the female lead protects the male lead. in kage kara, the male lead protects the female lead 

both series' respective protagonists have met each other since childhood, separated and are reunited at the beginning of the series, and the females are in love with the male, and all the girls have special powers and abilities, although the difference is wind is the drama version while koi koi 7 is the comedy version 

both series featured an only male student at ann all-girls school. however, tetsuro still remains a male in his clothing without cross dressing (except for one episode wherein he was forced to cross dress when his uniform was soiled by paint) while mizuho cross dressed in order to be able to attend.. 

a group of girls plus one guy and a homeroom teacher living together under one roof. the difference though is kono aozora is the drama version while koi koi 7 is the comedy version 

Similarities: Both have ridiculously corny storyline. Both were pretty much has a level of predictability. Both share the same action, school and harem genres. Both main characters all lived in a dormitory. Dissimilarities: One has Martial arts as it's extra genre, while the other has ecchi and mech ( mentioned only in other anime sites) as its extra genre. The muchacho (male lead) in KK7 is always the damsel in distress, while the muchacho (male lead) in Bento is a combination of being a wimp, asshole, nice guy and rabid dog (when he's going for-you know what) all rolled into one. Even if Bento has some ecchi in it, it is not as daring as KK7. read more 

one male student at an all female school 

koi koi 7 has an all girls school while sotsugyu has an all boys school except that sotsugyu has no females whereas koi koi 7 has one male  

one guy and several girls under one roof 

similarities: both series' male protagonists are a couple with the female protagonists and have known each other since childhood and are also wearing glasses differences: tetsuro tanaka (Koi koi 7) is immediately welcomed by the heroines and protects him while keitaro urashima (love hina) recieved torture on his first encounter with the heroines (except for shinobu who debuted in episode 2 and motoko who appeared in episode 3) also, sakuya kamatsuri and kaolla su seems to be both experts in weapons specially when the latter used a bazooka to chase off a disguised keitaro (they'd even make a perfect team) 

The female cast in both series is similar, and both are fighting series as well. 

Both are harem + fanservice + superpowered girls. The art style is similar as well. 

Koi Koi Seven has One Guy with 6 girls and in Rosario+Vampire One Guy with 4 Girls, It has a High Ecchi just like Rosario+Vampire. Those 6 Girls in Koi Koi Seven Has superpowers and in Rosario+Vampire Those Girls are all Youkai. But this is one is different Tetsuro Tanaka attended a All Girls school but in Rosario+Vampire Tsukune attend to a youkai school. One Girl is inlove with Tetsuro and in Rosario+Vampire One girl also inlove with Tsukune. The Six girls always care and protect Tetsuro, in Rosario+Vampire Tsukune also being protected by the 4 girls from evil.  

Same thing., Boy gets stuck in an all girl area. Also some parts of showing how much difference there is in strength from the lead male. 

school girls plus comedy = ) plus both series featured a show within a show that are parodies of super sentai series 

both series are ecchi themed, and have the female leads (chitose midori and yayoi asuka) falling for the male leads(yuusuke takasaki and tetsuro tanaka) 

both series are about comedy, and both male leads tetsuro tanaka and ryo mizuhara, and both female leads shizuka masuda and yayoi asuka are attracted to the male leads, though for ryo, it took a long while to accept shizuka while tetsuro immediately accepted yayoi asuka 

two series featuring 6 crazy and wacky girls.. give these two a crossover and surely, osaka might even imagine chiyo fighting alongside sakuya kamatsuri.. with the former using her pigtails as weapons(one pair of pigtails will be used either as joysticks for chiyo's jetpack, another pair as lightsabers, and another to hold a bazooka). also, hifumi and sakaki both loves animals specially for sakaki's case, cats 

Koi Koi Seven has One Guy with 6 girls and in Rosario+Vampire One Guy with 4 Girls, It has a High Ecchi just like Rosario+Vampire. Those 6 Girls in Koi Koi Seven Has superpowers and in Rosario+Vampire Those Girls are all Youkai. But this is one is different Tetsuro Tanaka attended a All Girls school but in Rosario+Vampire Tsukune attend to a youkai school. One Girl is inlove with Tetsuro and in Rosario+Vampire One girl also inlove with Tsukune. The Six girls always care and protect Tetsuro, in Rosario+Vampire Tsukune also being protected by the 4 girls from evil.