There is this fic I read some time ago. Sadly I forgot to bookmark it - and I don't remember where I read it.
In this AU story vampires are "out". Burt had a heart attack, in order to pay for a surgery and hospital Kurt agrees to meet Blaine a vampire and let him drink his blood. Kurt thinks that Blaine will drain and kill him, but to save his dad and his sister (Rachel?) he agrees. Santana was the one who offered Kurt the deal.
Other things that I remember:
- Kurt was terrified and had to shower before he actually met Blaine
- Kurt woke up the next morning and thought that Blaine would keep him as some sort of slave (but he was free to go)
- later there was a arrangement that Kurt let Blaine drink from him regularly
- Britt was a vampire too
It would be great if you guys could help me to find it again :)