I don't own Inu x Boku.
The Maison de Ayakashi is an apartment complex where those with youkai ancestry and/or from wealthy families resided there. However, there is only one resident who does not fit into the category, yet this person was able to take residence there away from people's eyes.
In fact this person was the very first one to reside in this estate before it was opened for the others.
Although this person did indeed come from one of the wealthiest families in the world, this person is also one of the most powerful beings possessing absolute power no one is worthy to have. This person holds a very special position along with a twin who shares a different power with the same acronym.
This person is said to be descended from a superior race that was once very much active until a certain disaster struck the dimension that lead to their extinction. The last two beings of this superior race then settled where humans and youkais coexist. Eventually they interbreed with them that led to this person and the twin.
Each twin inherited three youkai forms from their mother or ancestors. These three forms are known as Kuchisake-onna, Onryō, and Shinigami.
Unfortunately these forms caused this person to have an unstable mentality, but this affects this person living in the Masion de Ayakashi than the other one because of this person's association with the related title and position involving with the dead and the deadly sin of wrath.
Despite their youkai transformations and interbreeding, they remain full-blooded of a superior race with no traces of human or youkai blood in their veins.
None of the Masion de Ayakashi residents knew of the person's existence and the fact that this person lives in Room 13 on the thirteenth floor that is yet to be discovered of the rarely seen 13th floor button on the elevator.