Thanks for asking!
The Silver Asphodels fill out low ranks with people who are usually desperate or easily influenced, or they just yank people off the streets. For Complicated Reasons, Na'im was stranded overseas and ended up targeted for "recruitment" at around 16 or 17 and was forced to join the group whether he liked it or not.

As far as creatures they like hunting down, Bijan (the boss) mostly just follows the money. He doesn't fuck with ghosts or djinn but pretty much anything else is fair game.
Na'im hates hunting anything sapient - at least if they're going after a monster that's attacking people, that's doing something useful (even if it's making Bijan richer). For actual trouble, Na'im has gotten his ass kicked by any werewolf he's had to fight so those jobs suck.

He HATES his lifestyle/job/life/etc. He's still with the Asphodels because Bijan has broken his spirit and he's under enough controlling magic that he can't escape.