In Noxus (if you prefer another region, edit the message.), strength is all that matters and you were not the person chosen by the gods to be very strong, so, oppressed by others, you fled Noxus to another region, Ionia, an enemy region of Noxus, but much more peaceful.

Exploring the mountains of Ionia, you approached a small house made of straw until you came face to face with a man with the appearance of a samurai, drinking tea with his eyes closed and a sword kept at his side.

"If you are another one of those who came to "avenge" my master, leave before I cut off your head."

Said Yasuo, the Unforgivable.