From Mangahelpers:
Being an adolescent girl is just one problem after another. Middle-schooler Arihara Ayumi receives a note from a high-schooler, a very large and intimidating boy, Zaitsu Misao, asking her out. Frightened and intrigued, she doesn't know what to do!


-taken from baka-updates

Ah, the dream of 13! Kouta is our normal everyday boy, living with his fun-loving workaholic father. Lusting after the school idol in his class, playing games with his friends... there's nothing especially noticeable about him. But one day his father has to transfer to Sapporo and then appears a girl who volunteers to be Kouta's live in caretaker. And what a girl!

Everything about her is mysterious: her mysterious incredibly showy body, her mysterious interest in our boy, and her mysterious need to sleep in the same room...

Doki, doki...