As revealed by the official Genshin Impact account, "We Will Be Reunited" will be available to all players who have reached Adventure Rank 36, and who have completed both of the following quests:
- Story Quest: "Lupus Minor Chapter: Act I - The Meaning of Lupical"
- World Quest: "Chapter I: Act IV (Prelude) - Bough Keeper: Dainsleif"
"We Will Be Reunited" will appear under Archon Quests in the Quest Menu.
According to the mission description, Ganyu and Lan will inform you that the Treasure Hoarders of Mondstadt and Liyue have banded together. The plan is something to do with Abyss Order ruins, which naturally doesn't sound good!
Your job will be to investigate these ruins, but what you'll find is as-yet unknown.
This Archon Quest will be available after the daily reset (04:00) on April 12, 2021.