I can't quite remember the exact fic. I was reading ff for a long time before I got an account and started creating my favs list. But I think it was Dead and Dying by Losing my Reflection:
http://www.fanfiction.net/s/2135189/1/Be warned though, it's a vamp fic. But it's really good, and really angsty.
But my first full-out puppyshipping fanfic was Family of Dragons by Kaiba is WHAT productions:
http://www.fanfiction.net/s/1873209/1/One of the absolute best ffs out there! But, the authoresses only post about once a year... I'm not kidding...
For anybody else who reads this, they are rated M, so don't read them if you're not ok with it.