Tenshi and Suika is kinda like Akiha and Miyako... poor Tenshi :(

Fucking gross. Suika's ribs are pressing out from in her. At least I think those are her ribs, they seem too high up and small to be. Ew.

its the angle

There are a lot of tsurupettan characters in Touhou. Anyway, Tenshi isn't much smaller (if at all) than Suika. I don't know why she looks so defeated.

I think she's embarrassed, not envious.

She has her arms raised and kinda leaning back, so she's showing a lil bit of her belly and the rib cage, so it's the angle not the drawing, but yeah those are her ribs, why so bad? She's a cute slim drunk girl xD

It's a bad use of perspective, that's what it is. The image is done entirely too flat (no pun intended) to simulate depth, which is what that kind of perspective trick is for.