this pic is tagged with "bikini" and "swimsuit". but from the clothes laying all around her, the tie still around her neck, and the one half on sock, I'm rather sure she's supposed to be in her underwear/bra not a swimsuit.

if anyone else agrees with me I'll leave it to them to change the tags
(because I hate to change someones already well tagged post just because I alone disagree with a tag)

Yeah, I agree. This is "relaxing and oekaki'ing on a hot day after school", not "getting ready for the beach". Even though the bra isn't too detailed and could be mistaken for a bikini, the context makes it pretty obvious which it is.

Nice picture, by the way.

Bigger version (without the bra) from pixiv also uploaded.