YuriTenshi said: Geez, she must have crazy bad back problems...
Two things:
First: the 'back problems' shit is old and completely unfunny even about random images in other series or original characters. People who like huge breasts already know that, in real life, women suffer from abnormally large breasts more than they benefit from them. We also know that witches don't exist but interestingly enough, nobody keeps popping up on Marisa images to argue that. Seriously. Liking unrealistically large breasts is no less legitimate of a preference than the opposite.
Second: Your comment makes precisely no goddamn sense. This is Touhou and Yuuka is not a human being. She's a youkai. Youkai wouldn't have problems with their back, presumably, being superhuman. That old non-joke doesn't even apply to this image in any sense.
We really need more pushback in general against 'back problems hardy har' and might as well start here.
While I agree with LunarHunter, the boobs don't really look "right" here. I like Unadere's Yuuka pics where she has a more modest bust size by Yuuka standards. These don't do anything for me.
I also agree. Anyway, I read that the back problems due to having a large chest is more of a myth than actual fact. I have a friend who has pretty large breasts and has no back problems at all.