Thanks for the answer I would recommend watching these 2 videos as a jumping on point if you’re interested

The fist is this one by thehearthguy

This first one is quite long I know, if you’d prefer you can watch this one more digestible parts through other videos as this is basically a super cut of a while video series just talking about the factions in the game with relevant lore included as he goes if you want full lore those videos can easily get around 6ish hours

As for the second video that would be this one by FrenchesOP, though for a more in depth look at everything rhese videos can also easily reach 6 hours as well. Good luck

I think they have a fun and interesting dynamic as a couple or even just as friends with a fair amount of hidden depth mainly on elrena/larxene’s side

On Lauriam/Marluxia his search for strelitzia is great and also an excellent way to get him involved in the main plot, especially when they eventually find out she’s with sora (and potentially becomes Ava’s replacement on the master’s side if she turns out to be to old from being kairi’s grandma or to dead or to reincarnated as Kairi to be present) I would also love to see him meet namine again and try to make up for everything he did in CoM potentially seeing a bit of strelitzia in her, I would also be hyped to see him crash out if vanitas returns and he learns that he’s at least partially the ancient darkness ven trapped in his heart that struck down strelitzia

As for elrena/larxene there’s a lot to go over, first off her personality as larxene is really entertaining to watch especially for me as a fan of superhero media where the villains just straight up love being evil, but as we see a bit in both her character file and union cross to a lesser extent this super mean attitude is just a mask to hide that she does care because she fears losing the people and things she cares about or getting hurt as a result of them be it accidentally by those she cares for or by other using them to hurt her considering her cherished memories and those she cares for her secret, her chirithy even calls her helping lauriam in his search as being out of character in union cross, and of course her exchange with sora after she’s beaten in kh3 where she says who she was along for the ride for (marluxia/lauriam) is her secret partly because she doesn’t want anyone to know she cares about others, I also think it’s likely that when she regains her memory she might hate herself for surviving knowing she’s only here because she as in the right place at the right time and wasn’t supposed to be there in the first place, I would also like to see her mask slip and crack overtime as she spends more time with the guardians and learns that it’s okay and even a good thing to be open about how you care about others

If you want to get to know more about these characters and catch up on union cross lore I would highly recommend first damo247’s fandub followed by this dub of the character files story if you can’t get your hands on a copy of the book