Who is Yone?

He's Yasuo's brother, who Yasuo had to kill. The whole idea is that Yasuo was accused of killing an elder that he was assigned to be a bodyguard for when Noxians attacked Ionia. Yasuo decided to leave his post because he felt he would be more useful in the frontlines, but upon returning he found the elder dead.

The "symptoms" of the dead elder looked like he was killed with a win technique, Yasuo was the only one that really could use it that well because he was a prodigy at using the wind technique. Further speculation indicates Riven could have killed the elder whilst Yasuo was fighting in the frontlines or off doing something somewhere.

He gets hunted by every Ionian after he escapes Ionia. This includes everyone allied to the Ionian government. and to name a couple.

Yone was also obligated to hunt him down and kill his own brother, Yasuo. Upon meeting each other, Yone initiated the fight - even though Yasuo did not want to have to fight or kill Yone. Yasuo was forced to kill Yone to save himself from death.

Y-One