Since Concept/Beta TOH and Lumity is basically all a collective HC from the fandom using snippets of how the characters looked and acted from the concept art, imma just put out some ideas for plot difference and the way i feel Lumity's personalities and dynamic work in my head:

Amity
-similar to canon, but much more angry abt the fact she seems to be caring about Luz after each encounter

-*very* proud, more influenced by her parents in that

- whenever she does get the chance to fluster Luz she very much gets into it and tries to go as far as she can

-she tells Luz her feelings right before they get into a full fight, via asking herself "why does she wants to do this to the person who's been nicest to her ever despite being an ass" out loud and Luz prompts her to elaborate (ill expand on this)

(in relationship)
- is much softer and pretty caring when it's just the two of them. Still puts a tough front in public, but much less aggresive.

- she playfully bites Luz' knuckles whenever she wants attention (Luz plays along with it. "Hey when did a cat get in here?")

Luz

-similar to canon Luz in that she loves fun, fantasy and adventure, but more mellow in that she doesn't let Amity or people being mean to her go far; not afraid to fight back physically if need be, shaped up by how she's had to defend herself back on Earth due to bullies

-doesnt act as soft in general and puts on a tougher front in public, let's it down around Eda, King, Willow, and Gus as they're the only ones who she really trusts in the isles at that point

-She has a bat she carries everywhere and is not afraid to use it; She calls it Hecate.

- yes she's still a nerd and loves Azura

-her way of getting to the isles and meeting Eda and King and staying still p much the same but her more tough nature is what lands her into trouble with the guards n leads her to want to help out the comformatorium prisoners.

-in this au she meets Gus and Willow at the same time as they make their way to Hexside, curious abt their conversation she tries listening in but trips and falls into sight, Gus immediately recognizes she's human and attempts to befriend her, Willow also approaching curiously

-Willow and Gus' friendly personalities let her be able to befriend them easily, although she's still somewhat wary she decides to try and be cool with em.

-She meets Amity when Willow and Gus leave Luz to get to class, she was eavesdropping on them as she heard Gus talking about a human as she passed by

-Luz greets her in a more friendly way thinking she is maybe more like Gus and Willow, but quickly retracts herself when Amity+

rolls her eyes and releases a groan in disgust, asks her why a human is in the isles, Luz puts up her defensive attitude and they go back and forth. The start of their "rivalry". (I'll expand on this whole thing via a fanfic probably)

(Additional personality info)

-along with acting a little tougher she acts smug, but it's a sort of trait she has gained thru the years to protect her emotions and be able to fight back without showing her hurt emotions.

-kind of a romantic, tries to flirt with Amity when the chance and moment is there, and gets somewhat surprised whenever Amity *does* meet her energy back (she hides her flustered emotions pretty well with the mask of smugness though)

(in relationship)

-if she flirted before imagine now.

-teases Amity with spanish pet names

-she very much just cuddles or gives kisses to Amity whenever they're alone for atleast 10 seconds bc titan forbid ppl seeing them both act soft. (Amity teases her back over it.)

-she returns whenever Amity teases her by teasing her back abt how much she loves her and it goes back and forth. Luz usually ends winning the "arguments" (it's just them teasing eachother n being nerds for an hour until one or the other gives up lmao help them)

(I'll add more to this at another time and probably change things I've been writing and rewriting this for days )