4.148 out of 5 from 314 votes
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!
Both of these manga involve a nice guy who suddenly is introduced to the world of monsters - and monster girls. Being a fragile human with a quickly growing harem of powerful, possessive female monsters, and at the center of their vying for his affections, the poor guy can't seem to go one second without getting hurt by their aggressive love. Ecchi harem and romance elements are at every turn in Rosario+Vampire and Monster Musume - check the other out.
If you're looking for more monster girls in a less ecchi environment then giving Rosario to Vampire a try would be probably a good idea. Like Monster Musume no Iru Nichijou, Rosario to Vampire is a monster girl themed harem series, but unlike Monster Musume no Iru Nichijou, it's not borderline H.
both are about a group a monster girls that are in love with the same huuman and fighting over him, the difference between them is the location in rosario vampire a human is at a monster school and in monster museume no iru nichijou they are living with the boy
Both feature an ordinary guy being surrounded by a group of monster girls, which quickly ends up with him being put in all manner of dangerous situations as the girls battle for his affections.
Monster Musume no Iru Nichijou is borderline hentai, but if you enjoyed it then Rosario to Vampire may interest you. And if you enjoyed the story and characters, but weren't a fan of the almost hentai artwork then if may be a good compromise.
The Autana beast race is being hunted down by the Lizard Tribe, and only two mercenaries, the human Eita Touga and harpy Aero, have a chance of putting a stop to the threat. But some in the clan don't believe the duo has what it takes – who will win the battle?
Let's keep it short, the main theme of all the manga by Takamaru seems to be monster girls and guess what, both 12 Beast and Monster Musume no Iru Nichijou are monster girl themed. 12 Beast might not be borderline H like Monster Musume no Iru Nichijou, but it's still ecchi, so keep that in mind if you want to pick one of those manga for reading.
Both of these manga are written by the same author, and both just happen to be about monster girls. Monster Musume no Iru Nichijou borders on hentai a lot of the time, and while 12 Beast never goes nearly that far it's still definitely an ecchi title.
If you're looking for more monster girls or want to read something with monster girls that is less on the H/ecchi side than Monster Musume no Iru Nichijou, then Centaur no Nayami might be just what you are looking for. Note that while it's not even an ecchi manga it's odd, might cause you to rise a brow and lets not forget the shoujo-ai vibe.
If you want a much cooler take on the monster girls theme than what you can find in Monster Musume no Iru Nichijou, give Kaibutsu Oujo a try. The girls there are fairly cool and the harem part never really kicks in.