For a manga about peeking at panties and ogling female classmates, the artist is really horrible at drawing skirts hanging over hips and just draws buttcheeks and a crack and expects us to assume that underwear is there. But based on the art alone, I would have to assume all these girls are going to school commando. The only reason I know the author intends for us to interpret them as wearing underloons is because the main character comments on their color. We do see a scene of a gym class where all the girls are wearing tight-fitting, cameltoe-creating bottoms. The story's extremely bland, just feeding into the author's apparent voyeuristic fetish, with its only twist being the idea that there's a girl who also enjoys ogling other girls. It's douchy behavior whenever a group of bros rank women, and it's no less douchy when a girl joins in.