I probably don't wanna know but like what has Aku done with Luci? he doesn't seem interested in her I'm confused.
Luci's dad is awful, yes? So as a kid she immediately latched on to Aku, who didn't really even have to DO anything. Just by existing and letting her crawl all over him, he's shielding her from her dad.
As she gets older he has to go out of his way a little to earn her trust (since a 15 year old is more psychologically complex than a 7 year old) but he still doesn't have to do much at all. He feeds her obvious crush on him in small amounts to make her THINK he isn't all THAT interested which makes her work harder for his attention (which she already has).
And whenever Aku has a new "playmate" (girlfriend) that he's using/abusing he tells Luci about what his actual plans are to make her think she has his secrets and she's the one he really trusts. When in reality SHE is the one he's actually "playing" with. Aku also knows she's a little blabbermouth sometimes, so in that comic I did, he is feeding her information about Ashi's mom that he KNOWS Luci will repeat to her, because he figures it's about time for his High Priestess to fuck off and have their kid so he can chase them both down and do what he's gonna do.
tl;dr He is VERY interested in her, in every way you can think of. It's mostly that he's fascinated by her, but she's cute, too, right? Why NOT groom her into becoming his ride-or-die, his closest confidant, his partner in crime and personal assistant? It's how he makes life fun.
However he did NOT realize what he was signing up for, which is being shadowed by a literal troll from hell who shows affection by getting on your last fucking nerve.
It's a "be careful how you treat your kids because they will cry for help and you don't know what might answer them" scenario. Same deal with Ashi except Aku is her real dad