>>279756451A "normal" girl in the west (not US. west) would be considered overweight in Japan.
Ideas and expectations of both genders is to be thinner than the West.
Most girls in picrel would be considered 'thicker than normal' and not skinny by jp standards. Only one that passes as normal would maybe be the girl at center.
Japan just smaller as a country, people eat less, and live longer. Not better or worse.
So in the case of the manga. Girl is "chubby" or overweight if not outright fat by jp standards. But japs have lots of otakus and there are fetishes for everything.