Did you ever have plans for Lilli's character development? like giving her a Semblance or some sister bonding between her and Robin?
It's funny, I actually recalled Lilli's character development two days ago on discord. Literally one of the next scenes in Arc 4 was gonna be Lilli confronting Robin (pic of an unfinished (yet surprisingly coherent page below)):
The sum of it is that Lilli gets up at night to get some air and finds Petra grabbing water in the kitchen. She's on surprisingly good terms with Petra (probably has a crush on her and Petra's PJs consist of an oversized t-shirt and knee socks so let's be real here) and Petra affirms that Robin & co are still in Mistral despite learning about Zenith (the Braith's base), and that Robin told everyone to get a "good night's sleep". This is the final straw for Lilli.
Lilli grabs her labrys and attacks Robin, waking her up. Robin and Marron are still miffed so Marron isn't there.
Here's the full scene:
In retrospect I think this development was maybe sort of rushed, as a lot of things were as I grew to be a better writer and realise that characters actually need arcs... but that's a symptom of me being tired and just wanting to get to the RAIN finish line as soon as I could (spoiler: I didn't make it)
I think it's no secret that Robin, and by extension a lot of the protagonists, can be shitty people. They're not paragons, they don't communicate, sometimes they're more self serving than they should be, and Lilli is a by-product of that.
The sad truth of Lilli Lincoln is that no one likes her because she's mean, but she's mean because no one likes her. Her siblings are all adored and love each other (except maybe Wil), and she's acutely aware that she's literally the Least Favourite (which raises questions about Orion & Artemis's parenting).
As a kid, she was fuelled by envy because she didn't understand why her siblings all liked each other and were treated better, and it festered into spite the longer she was ignored.
There's a (somewhat) happy ending to this all, though. As the end of the scene implies, she and Robin have a vaguely more amicable relationship going forward. In what few scenes Lilli had before RAIN leave for Zenith, Robin would try to involve herself more in Lilli's future - encouraging her to sign up to combat school. Lilli points out some blatant issues in Robin and Marron's communication that puts them on good terms again.
Lilli is also very aware of Robin actually making an effort to know her, so when Marina phases through a wall and tries to edge in on the banter she utterly rejects it with a pre-written speech.
"Please do not attempt to make light conversation or banter with me. You are still complicit in my neglect for your own reasons, and are, therefore, an absolute carbuncle. I forbid you from attempting to take a shortcut by hijacking the effort Robin has made."
In the long run I think Lilli's life gets better. She's still a bit of a snot but she actually begins to form relationships with her siblings.
Also Tahlia Braith was super gay for her so that's fun.