Technically, a girl. But just technically, the meaning of that symbol in her head could be taken in many ways.
Just like Uboa, which instead of be taken as a personification, be taken as revenge.
Poniko is the emotional side of Madotsuki, locked away in her subconscious. That's obvious, since it's really hard to get to her place. Because she's locked away, bothering her (turning the lights on and off) causes Uboa to appear. Since it's meant to give a fright to the player, it could be interpreted as a revenge from Poniko. Trying to touch Uboa leads you to a very frightening place, as well, with a very erotic background. Analyzing this picture, could give the results of a bad sexual experience, which could be why Madotsuki locks her emotional side away. The FACE, Monoko, Monoe, Sekomumasada, they're all Poniko, just in different forms.
So yes, they're all girls. Now, what they're supossed to mean to Madotsuki's self, could be her Feminine, her Masculine, her Herself, it's all different sections of her subconscious. Or maybe I'm just over thinking it.
