Danbooru-based image board with a specialization in high-quality images.
asahina_mikuru bike_shorts koizumi_itsuki kyon nagato_yuki suzumiya_haruhi suzumiya_haruhi_no_yuuutsu

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Looking very K-On! there Koizumi.
bloomers - skin tight, no leg
bike_shorts - skin tight, with leg

suzumiya_haruhi_no_yuuutsu - k-on! crossovers/parody are quite normal, but it is usually the girls, not Koizumi on his own.
This is official art, I'm guessing? It's probably just something drawn by horiguchi_yukiko and not meant to be a K-ON! crossover/parody.