More from this AU, which has turned into something totally different by this point tbh.
So the premise is basically the same as before, where Kairi and Naminé run off to find a way to save Sora post-KH3. Kairi visits all the PoHs (old and new) to better understand her own powers.
Early on in this adventure, they run into Larxene, who's spending most of her restored life fighting hoards of heartless whenever she can find them. Larxene actually misses not having a heart, and she loves committing violence, so she figures that even if she gets overwhelmed in a fight, she'll just get to be a Nobody again.
Anyway, Larxene tries to pick a fight with Kairi, but Naminé defends her by using her memory shattering ability just enough to crack Larxene's heart. It doesn't totally disable her the way it did Repliku in CoM, but it does significantly weaken her powers to the point that she doesn't really pose that much of a threat anymore. But the worst part of it (for Larxene, anyway) is that she won't become a Nobody again if she loses her heart now that it's in the state that it's in, so she's stuck being a human.
So Larxene then spends most of the rest of the story basically trailing the other two, occasionally picking very one-sided fights and generally just being a nuisance.
Once Kairi's learned more about her PoH powers (so that she can use them consciously rather than automatically), she offers to use them to repair Larxene's damaged heart, which is what's happening in this comic.
I'm not sure what would happen afterward, lol. Like Kairi, Naminé, and Larxene definitely aren't BFFs by the end of the story or anything, but I guess Larxene would have teeny tiny smidgen of respect for the other girls' powers in the end.