claimed buffy/grows fangs

I read a fic about buffy starting out as the slayer but spike claimed her and she started to grows fangs. It took place around harsh light of day, and now I can't find it. Help me please

Sounds like Jackofspike's stories. I was going to say either Penny for your... But that isn't the right time period but Chosen after Death could be it. Could also easily be Maryperks stories too...especially her Immortal Guardian Series.

I've read something like this on Elysian Fields, but an older fic. You might want to do a search for Season 4 and claimed or with bloodplay search here

It could be never be the same again by maryperk
Buffy enlists Spike's help for revenge against poophead Parker. What happens when Buffy asks if she is still Spike's girl? See how becoming Spike's mate changes Buffy's life forever. This story has sexual situations between Spike and Buffy; please be warned.

Both of those stories are great! And both are start during Harsh Light of Day. There is another one that is set in season 6 called Time of the Guardians, where Buffy comes back after Willow does her spell and her and Spike mate and she grows fangs.