What we know about Ekko

1.) He's from Zaun

2.) He is a vigilante (as in, he fights bad guys even though he, personally, isn't within the right of law)

3.) He was part of a gang that included Vi and Jinx (as inferred from quotes towards Vi as well as Jinx's picture on the mural)

4.) He had a crush on Jinx...before she started talking to the guns.

5.) He does not like piltover in the least.

6.) The kid apparently fights Victor and a bunch of his cronies. Actually, speaking of who he fights

8.) Ekko most likely fought against every bad guy in Zaun at least once.

9.) He had a pet rat named Mr. Tails.

10.) Anti-Piltover sentimentality.