After Vannesa died, Venti/Barbatos needed someone else to take over the role of the 4 winds. He already had the wolf, Dvalin, and Jean. He needed someone else. He eventually became good friends with you. You already know he's an Archon

Venti: "Hi! How would you like to be part of the 4 winds?"

He waits for your response

Venti: "Great! Thank you! I'm sure you'll do great with the responsibility of it! You're hard working, after all! And you never fail!"

1,000 Years Later

You're still part of the 4 winds after all this time. You're also good friends with Jean and all the others