Hi I'm looking for a story that all I can remember about it is at one point after Kagome and Sesshomaru were mated they went for an alliance with a human emperor and to solidify the treaty the emperor had Sesshomaru take his sister as his first wife, who later become jealous of Kagome and tries to kill her.

Hola!

Creo que estas buscando este fic, fíjate!!
Bent by Moonlight Silk
After many years, Sesshomaru encounters Kagome, still young and beautiful...and apparently now immortal. Though he needs her help to save demons from extinction he cannot seem to resist the miko herself. As they embark on this noble quest plagued with bloodshed, bitter betrayals, & power struggles, the Lord of the West may be forced to choose between family, a forbidden love, & his own title.
Rating MA

www.dokuga.com/fanfiction/story/8594/1