Nimbus introduces themself as the "Rookie Cloud Strider" in Neomuna. Nimbus, their superior, Rohan, and the long line of Cloud Striders who came before them have been keeping the city and its citizens safe for a long time sans-Guardians. Nimbus isn't sure what Guardians can bring to the table now, but it seems Neomuna and the Vanguard have similar enemies. It can't hurt to work together, right?
Complete the mission "Under Siege" in Neomuna.