This is extremely good; it perhaps needs editing a little, but you've captured the style of the Celtic myths very well. I love these myths, and I'm very impressed with this one! If I were to give some critisism, it would be that the ending could maybe do with a little more description of the shows of grief of the king, Buan and Fainche - "for they had loved her very much" or something. I'm not very good with this sort of style, but you obviously are, and, either way, this tale works very well as it is!