Yzme (hound mc) doesn't know enough birds to make a suggestion herself. She really only knows seagulls, and if Ais (or anybody) called her that, she'd throw hands. lol
it's hard to pick a bird for her bc look wise (like color matching) she could be a purple martin. Personality wise- it doesn't sound cute, but a goose. and skill set wise- a hawk or falcon. So Sparrow it is. lol
Aelia (unnamed mc) would be a parakeet. Ais would see her and Kuras together and call them the lovebirds.
Halcyon (alchemist mc) honestly hates the nickname bc they are the kind of person who's like "refer to me by my name or don't refer to me at all." But a Starling would fit them.
But to go off the tags for moment:
I think Ais picks his nickname for multiple reasons- personality, looks, occupation, his own feelings/view of the person, etc
Sparrow for MC since sparrows are 1. neutral in color so they can fit any MC and 2. sparrows can be pretty feisty which lines up with how MC acts. (personality) BUT ALSO they are just a small common bird so they don't really have anything to stand out. But Sparrow makes for a good neutral but nice sounding name.
Mhin is dove bc of their white hair (looks)
Kuras is referred to as The Doctor. (occupation)
Leander's nickname is Pretty Boy. In my experience/observation, calling someone a pretty boy is usually done in a condescending manner. I feel like Ais picked this nickname bc he doesn't take Leander seriously (Ais's own feelings), but it also doesn't sound like a complete insult at the same time.
Vere's the only one we don't get a nickname for. When Vere is the topic of conversation, Ais just refers to Vere as "he." Either bc Vere wouldn't/didn't approve of a nickname, or Ais had a nickname for Vere and stopped using it bc he became too attached then backed off.
And yes, I think Ais gives everyone nicknames to stay detached from them. Names are people's identities, and if you don't know/use someone's real name then losing them might not hurt as much.
Like "No, MC, the beautiful person who appreciated/helped/accepted me, didn't die. A common sparrow died."