Tokido Saya

In the daytime, she is a popular girl in her class at Riki's school due to her attractive face and figure, though is known to be a natural airhead. However, at night, she can be found at the school wandering around in order to protect a "treasure" from those she calls the "darkness executives" and even has to fight them for it.

Spoiler

Her real first name is Aya(あや)