>Aqua
She probably spends a good chunk of the day with her hand down her pants, absentmindedly playing with herself as she browses the net watching videos or waiting in queues for games. One of her hands is probably permanently marked with the scent of her snatch as a result.
When she really gets in the mood, she probably gets completely naked because her autism makes it impossible for her to concentrate if she has clothes on that are rubbing all over and getting gross and sticky. I'd guess she loads up an eroge or something and just starts firing away once she gets to a scene with her favorite heroine. At other times, she probably does it on her bed (again while completely naked) after reading over some of the hot and steamy scenes in her shitty harem LNs and closes her eyes to fantasize being in that scene. She probably goes at it rough and rapid, like a jackhammer, with as many fingers as she can fit, which is two, because she learned all her masturbation tips from the internet and from self-teaching, never bothering to learn about the more "sensual" ways of pleasuring yourself. It's likely she ignores playing with her breasts or stimulating her nipples and probably focuses almost all her efforts on working the clitoris.
She's definitely a moaner and probably starts yowling like a beast in heat when she gets going. Usually she tries to satisfy her urges when Kumiko isn't home, but obviously that's not always possible so sometimes she has to stifle her moans to the best of her ability, maybe by trying to cover her mouth with one of her hands or burying her face in a blanket or pillow. Of course, even then, sometimes she'll make a mistake and accidentally let one slip. Kumiko pretends not to notice and Aqua still thinks she's never been caught.
She definitely has used the shower head to masturbate on multiple occasions.
