Moriko and Atsuki are cousin. Atsuki's parent have to go to work abroad, so he has to live with Moriko's family and now he works as a Biology teacher in same school Moriko attends. Atsuki is really good looking, and everyone is jealous about Moriko that she lives in the same house with him. However, regardless of his good looks, Atsuki has some odd quirk that can make people's speechless sometimes.
He is quirky, random and simple minded but he is also intelligent at the same times. Atsuki loves the story of Sherlock Holmes. He likes anything that sounds exciting and intrigue him as an interesting case, this always cause him, Moriko and Moriko's freind-Hikono to get involves in mysterious cases.