A being that forgoes life for eternity, and an eternal being that surpasses the limits of logic and became mortal. What a good match.

Well, Cirno is still immortal :V

Well for Cirno and most faerie they don't have the best memories so the next day is always a new one.
And then you have another who's hell bent on revenge about something eons ago and never lets go

It's heart-warming seeing two immortal beings being friends . Most youkais in touhou are immortal but Kaguya and Cirno are the popular case

AjmolHussain said:

It's heart-warming seeing two immortal beings being friends . Most youkais in touhou are immortal but Kaguya and Cirno are the popular case

Most of them are certainly not immortal, including Cirno. Kaguya and Mokou (and possibly Eirin) are the only truly immortal characters in Touhou.