Edward is jackdawvision, a little play on the AC franchise's iconic Eagle Vision and the fact that Edward is associated with jackdaws instead of eagles
similarly, Jacob is rookvision for the same reason, except his association is to rooks instead - his gang is called the Rooks while Edward's ship is called the Jackdaw
Noctis has two usernames - I play his older version in Kaisou, and his username is illucesco, Latin for "to begin to dawn", which alludes to the ending of FFXV and his storyline in general. I was very proud of myself for getting this username tbh
his younger version uses fisherprince, which is a play on the concept of a fisher king - a well-known figure in Arthurian legend who embodies his lands, so when the lands suffer he suffers. he also fishes a lot. obviously I had to get the fish username for the fisherman.
March 7th has trailblazingspirit bc she's on the Path of Trailblaze and one of the more spirited and enthusiastic characters in HSR. if I ever figure out a different username for her I might switch it over to that but for now I'm satisfied with this