I think it's an anime that you didn't watch and probably you even don't know XD. It's from 'Sekai ichi hatsukoi', a yaoi anime, and this Yukina guy is in one of the side pairings.

I really love that character! I think that in SAO, Yuuki is one of the best character *-* Regarding Asuna, for me is not an "incredible" character; in the first part of the anime yes but then her role 'loses' something for me.
Fyi: 'Mine' Yuuki comes from 'Code: Breaker' and this is the second anime that I ever watched.

I don't know why I'm telling you all this hahah gomen XD