Fifteen-year-old Tsukune Aono is average in every way; he has no hobbies, less-than-stellar grades and he's even flunked his high school entrance exam. His parents have managed to enroll him in a school, but it's no ordinary school! Tsukune will be attending the Youkai Academy, a place where monsters learn how to co-exist with humans! As the werewolves, vampires, witches and other monsters are required to retain their human forms, Tsukune - the lone human - is able to avoid their bloodthirsty gazes. However, he quickly attracts the attention of a number of devilish beauties including the vampire Moka, a busty succubus and even a young witch! It seems Tsukune's average life isn't so average anymore!
In world where flesh-eating monsters roam the streets, only one organization has the means to save civilization from annihilation: Red Shield, a specially-organized unit designed to fight these monsters, and the only weapon that can destroy them: Saya. Awakened from a 30-year sleep, Saya is thrust into a modern world which she has no memories of, and is troubled by a past filled only with bloodshed and sadness. With the undying love and support of her family and friends, she struggles to gain the strength to move forward and regain the pieces of her shattered memories.
If you liked Rosario+Vampire but also want a deeper storyline then try Blood+. Both series include a female lead (Moka, Saya), that is a vampire who's personality changes when in battle and a male character (Tsukune, Hagi) who help them get in to their battle personality.
Boku wa Tomodachi ga Sukunai reminds me a lot of Rosario to Vampire in the sense that the male protagonist is in search of friends in a new school. Both shows are centered around school life and full of comedic moments, but Rosario to Vampire focuses more on action and romance than Boku wa Tomodachi ga Sukunai does. You can expect otaku references, laugh-out-loud moments, ecchi scenes, and even tons of moe in both shows as the male protagonists tries to live out a normal everyday school life.
Some things in life are so bad that you'd like to pretend they're just a dream. Unfortunately for Kazuki, trying to save a strange girl from being brutally killed by monsters (and ending up dying instead) is an unfortunate reality. Out of pity, the girl replaces Kazuki's heart with an alchemy-based artifact known as Kakugane, so that he may live on. With this strange device, Kazuki gains the power of Busou Renkin -- Arms Alchemy; a power that will come in handy when monsters (and worse) begin to plague his town! Kazuki soon meets the girl from his “dream” (named Tokiko) in reality, and she tells Kazuki to get on with his life; but with his sister and friends in danger, that might not be possible. Besides, if Kazuki gives up the chance to show off just how manly he can be, how can he hope to win the heart of the alluring older-sister-like Tokiko?!
Having failed to earn admission to a university, Hideki Motosuwa has moved to the big city, determined to study his hardest for next year's exams. However, an unusual distraction presents itself one unsuspecting day in the form of Chii, a robotic young girl that has been discarded in the trash. In a world where an increasing number of people turn to these 'persocoms' for company, the bonds and limits of human relationships are tested as flesh manages to fall in love with the machine itself...
Both anime's follow a similar style. Chobits is a little more innocent in terms of sexual scenes where as Roasio to Vampire's sexual scenes are literal. Both anime's can be geared towards both males and females, though I believe males might find these two slightly more enjoyable. There's a few cutesy moments in each of them but the majority is literally mindless sexual references backed up by a minimal plot line.My recommendation is that if you don't mind sexy anime's then give these two a shot.
Shido Itsuka was born in a world where widespread catastrophes of varying size called spacequakes can happen anytime and anywhere, razing everything in the vicinity. When his city's alarm forewarns one impending, the teenager races to his sister Kotori in an attempt to rescue her. But upon his arrival, the spacequake transpires in that very spot, and standing in the middle of the destruction is a beautiful sword-wielding girl. Soon after, he learns she is one of many beings called "Spirits" who cause the disasters, and charming those like her is the solution to preventing them. Effective immediately, Shido must date Spirits and make them fall in love with him, because if he cannot, mankind's destruction may very well be inevitable.
A male lead surrounded by powerful supernatural creatures who so happen to have an attractive female figure. Actually the female figure is probably a main character in it's own right in both anime as it get's a lot of focus. Both series sport a token loli-type girl while the rest are considerably endowed. In both series the male lead is very much the underdog powerwise but Date a Live gives the male lead some survival tools while Rosario to Vampire's anime does not. The premise in both series revolves partially on not pissing of said powerful girls however that's where the similarities end, both have very different settings beyond what I described above but both rest firmly in the harem genre.