Akai Ito is set in the present age, the game unfolds from the point of view of Kei Hato, a girl who has a special blood called "Nieno Chi". A special system called the blood sucking system is used. Aoi Shiro is an adventure game that sets stage in both the modern real world and a mythical world. Aoi Shiro takes place in the same universe as its predecessor, Akai Ito.