From the Animeraider:

Three new students have transferred to Toudou Jirou’s private school, all siblings, and one of them is his roommate. They’ve been sent to try to live as “normal humans”, whatever that’s supposed to mean. After all, they’re human themselves – although they certainly seem overly confident of themselves. Of course, it turns out that these three siblings are much much more than they seem, and they’re about to throw ordinary school life upside down…