The blouse is thin and probably wet from sweat, this should explain why you can see the nipples. As for why her breasts aren't sagging? That's because her breasts are firm due to her still being young.
Summer... Flash! Run straight ahead with all your might. Until one day, you'll catch up with that person.
Though sadly, Sakura will never catch up with Ryu. It'd be cool to see an older, more experienced version of her (though still with the same spunky personality and short hair, I hope) but we never will...