Wow...just finished Volume 1 of Claymore. Nice to read something for the first time that affected me emotionally like this!
Claymore Vol 1 Chapter 4 spoilers:
||So apparently Claymores eventually become full blown monsters over time, and when they feel they're close, they call a black letter, which essentially is a request that another Claymore end them before they become one, and can die as a human.
In the final volume Clare has to kill her best friend, with the friend that she's made begging her not to do it! It's so tragic!||