The medicine that Tohru gave to Kobayashi in chapter 42 returns in chapter 35 of Kanna's Daily Life, with Kanna spending a day sporting cat ears after mistaking it for a supplement drink.
Takiya and Fafnir may have a very close friendship past a certain point in the story, but it feels legitimately believable and honest rather than a pair of boys who just got shipped together for the hell of it or anything put into a sexual context.