Sousake Yubiwa, also known as Sousake the Artiste and the Chairman, is one of the main characters. He is a member of the  Pretty Boy Detective Club and the heir and de-facto chairman of the Yubiwa Foundation, the organization responsible for the management of Yubiwa Private Academy.

Sousaku is a very quiet and taciturn individual, almost always choosing to stay completely silent, and even when speaking, he is usually does so quite faintly. Sousaku does have occasional moments where he will declare something out loud in a full voice, taking Mayumi by surprise.