Shounen manga serialized in Jump by IKEDA Akihisa.
Synopsis from mangaupdates:
By a bizzare coincidence, Tsukune Aono has accidentally gotten himself admitted to a youkai acadamy, a school attended by monsters (youkai). Just when he thinks he'll run away from there, he meets the beautiful girl Moka and his mood turns ultra happy. However, she transforms into her true form when the rosary on her chest is taken off, she's a super vampire!
------------------
Not a bad manga. It's not exceptional or anything, but it's entertaining enough. It does have some very typical shounen moments, but the artwork is good enough to keep me reading.
And the plot thickens in volume 4 and onwards.