There exists an official manga adaptation of G-On Riders. It tells basically the same story, with two key differences: full-frontal nudity and lesbian foreplay.

When I reached the hot-springs scene where Yuki and Yayoi lick melting ice cream off of Sela’s body, I had to go look it up to make sure it wasn’t a doujin parody comic. No, it’s legit, and it’s ecchi, and in the final battle, every female character in the series is completely naked.

Yes, them too.