Soto no Kuni no Yome (そとの国のヨメ, Foreigner's Bride); 2011-04, 06, 08, 10, 12, 2012-02
Touji is your regular run-of-the-mill high school student, he only has one particularity, which is that he knows Lufu's (the class resident tsundere) biggest secret: Lufu happens to be a succubi who periodically needs to get energy from males in order to survive.
While (initially) Touji had some wild fantasies, succubi being sex demons and all, Lufu can actually get someone's energy simply by holding hands or via hugging... But even if that much is enough, Lufu seems to be getting weirder and weirder after every "meal".....
At the same time, we have that the stranger Lufu seems to be getting, someone else is also acting weird, and that would be Tamao, Touji's handsome male(?) childhood friend, perhaps he(?) has a secret as well?