From MangaHelpers:

The Kemuyama family has just moved into town. From the outside, they seem ordinary. The family consists of a breadwinner father, a chubby mother, a teenage daughter Tara, and a video-gaming little brother Kemuo.

What no one knows is that it is all an act. These four people aren't even really a family; they are four complete strangers. They were hired into their respective roles by a mysterious group they know only as "Tako-Pon." They're supposed to behave just as a normal family would, and to avoid discussing their individual pasts.

When some of them bend the rules of the contract a little, letters of admonishment from Tako-Pon begin to arrive, making it clear that they are under very close surveillance. These letters eventually vanish, leaving no evidence behind. What is Tako-Pon and what does it really hope to gain from these people? [tethysdust]