This is reminiscent of a drama track that was on IOSYS's recent CD "Chotto Matten." Youmu was about to send Yuyuko to bed, when Marisa flew by, randomly showering sparks everywhere. (Does she even look where she's going? no.)
One of Marisa's sparks crushes the roof, and Youmu gets a few scratches. Yuyuko begins flustering over Youmu's injuries, ("Don't worry, Yuyuko-sama. I can cure a scratch like this just by licking it." "Oh no, licking it isn't- wait, is it delicious?" "Uh... no, it's not delicious, but-") and flies to Eientei to get medicine (where another terrible ruckus is going down). Tei slips in some "suppository" with the medicine Eirin prescribes, and insists Yuyuko read the instructions before administering it. Of course, she doesn't.
After making Youmu drink the whole bottle, you guessed it, she grows to gargantuan proportions. Just in time, Marisa comes flying back and has to fight with the giant-sized Youmu who takes some collateral damage. ("Youmu, she shot a hole in your panties~! I can see right through them!" "Yuyuko-sama, please don't look anywhere inappropriate!")
Anyway, what a long, needless story. The oversized Gensokyo girls thing seems to be a trend though.