I too find that most k-pop idols carry more weight in their legs, and I would guess that is due to all the dancing, especially since many have been dancing from a younger age and therefore have built up more muscle in the leg and namely thigh area.
There are some exceptions to this, however, I find Yukyung from Elris to have nice legs actually, and although she is around 5'1 she's said to be 81lbs.
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I like her doll-like look and I think her arms are nice and graceful.
Doyeon from Weki Meki has a nice body shape too
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I don't really think she's sg skinny, mainly because of her more muscular legs but I like her waist shape.
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Honestly, I struggled to think of many idols with slim thighs, many will have skinny calves but less so in the upper thigh area. Maybe because of muscle, and in general, I think most have toned thighs from dancing and such. Although these aren't really my goal body I can at least admire aspects of it. I think in general k-pop idols have very nice waists.