Mayuki's maid. Mayuki once said that Hatsumi is always in a hurry to find him in the house that she trips over her own feet, which she will subsequently let out an outrageous scream.

Spoiler

It is later revealed that she is one of the two "dolls" that Seiran controls. when in her aya or doll form she fights using her hair as a whip.

(Source: Wikipedia)