Behind the Scenes #56 (Patreon)

Chiyoka's reference sheet. 

She's the tomboy-type and her clothing choice is pretty simple. Her school uniform is different because she goes to a different school (duh :p). You can kind of notice how the SAG she's wearing is very tight even in the reference.

Nothing much to say on her summer outfit other than she really likes the t-shirt, she actually thinks it's cool to have "bad ass" printed on it. To further express her tomboy-ness she's wearing trunks even with her swimming suit. Her pajama is kind of girly because, as you've seen in the mountain chapter, when Chiyoka sleeps she lets out her innocent side.