Yone, the Shadow Samurai is a custom champion.
In life, Yone was a benevolent swordsman. He once trained in a renowned Ionian sword school along with his brother, Yasuo. When Noxus invaded Ionia, he went to war, while his brother Yasuo stayed guarding an Ionian Elder. After returning, he discovered that the Ionian Elder was murdered, and that his beloved brother was accused of the murder. He pursued him because he felt that it was his duty to not let his brother continue his possible misdeeds, but when he confronted him, Yasuo killed him.
After his death, Thresh captured his soul and took it to the Shadow Isles. There, his soul was tortured until his will was destroyed. He was then resurrected as an specter, but he has long forgotten his friends and loved ones, and there was nothing left of the benevolent man he once was.
Now, consumed by the Black Mist, Yone just wants to serve the Shadow Isles, and seeks the living to bring their souls to his new home.
In service to the Shadow Isles, Yone traveled back to Ionia. He attacked a fishing village, and the destiny wanted Yasuo to defend it. Once again, the brothers were forced to fight each other. Yone didn't even remember him, but it was like a nightmare for Yasuo.
Days later, Yone found Yasuo again. For the first time since the invasion of Ionia, they were able to hold a conversation. Yone told his brother what happended to him and what he did while he was not himself, while Yasuo convinced him of his innocence.
Sided together, they will first prove Yasuo's innocence. And then, they will fight to end the Black Mist once and for all.