How long will it be until we uncover the 4 yr mystery?

More importantly, how does and know .

My current theory is Vi and Jinx were childhood friends, but Vi hit those edgy teenage years where it wasn't cool to play with kids anymore. So she left Jinx, who now didn't have any friends anymore, as Vi was the only one willing to play with the "weird kid." So all of Jinx's current stunts are her trying to play with Vi again, who has just simply forgotten her old friend. The blue hair and being bat-shit insane doesn't help.

I've legit never seen anything from riot that says they knew each other. Vi is a perfect target for jinx. A hotheaded, ex-gang member, cop. Who better to piss off.

Vi is Piltover's best know law enforcer along with Cait. Jinx hates Piltover's law enforcement. If it's anything deeper it hasn't been revealed yet.

Sisters from the same gang

Riot Ghostcrawler confirmed that and are sisters.

Source: https://www.youtube.com/watch?v=20lcWfD58Vc&feature=youtu.be&t=1h13m33s

Well lore was rewritten and pretty much revoked so idk if thats even a thing anymore or this is just like kogmaws father/kassadins daughter

Here's some food for thought: "On his deathbed, a notoriously mad sump-scrapper claimed to have found Vi adrift in a bassinet large enough for two in the ruins of a collapsed chem-laboratory."

It's safe to assume that Vi definitely has or had a sibling. Whether or not that is Jinx remains to be seen.

Wait did they change Ekko, Vi, and Jinx being childhood compatriots?

Jinx and Vi were both trouble making youths of Zaun. That alone is probably reason enough for at least Jinx to know of Vi.