Ooh boy this thread hasn't been talked on in a while. Here goes.
- Peacock and Black Dahlia are related. Not much information is given to us about Dahlia's life before she became an Anti-Skullgirl Weapon and then criminal in turn, but this headcanon sort of assumes that she had a more mundane life before getting uhh.. put through the skullgirl cheese grater, but anyways. Basically, she had young children at the time, and due to OBVIOUS mental illness, when she became an ASG, chose to kind of forget they existed. Well, before the war between the three major nations, Peacock's parents fled the Canopy Kingdom to Romellgrad, thinking they could escape the inevitable war. We all know how that turns out. Basically, this makes Peacock's grandmother Dahlia. I know most of Peacocks'.. Issues.. come from her experiences in Romellgrad + the Medici, but it would also be pretty interesting to see a "crimes of the father" type trope with the two, where Peacock finds out about Dahlia's existence as her grandmother in some way and swears up and down never to become like her. A violent, rabid beast with an insatiable drive for pain and battle.
-Leduc is not a confident person. We don't get much information on Leduc, but I'd like to think he's very nervous at times. I have a headcanoned backstory for him as well, but who knows if we'll get more information on him, so I'll keep it to myself. Basically, the lab has really been all he's ever known, so he's terrified that he's going to let them down or disappoint them in some way. Hence forth, anxiety.
- Eliza and Dahlia are very very gay. I'm not elaborating.
- Avery is like a real pet bird and LOVES head scratches.
- Idk if this is confirmed or not, but it is my opinion that the kids in the background of Lab 8 are the children from Romellgrad. Peacock constantly shows off and impresses them. She also cares a great deal for them, considering she took care of them alongside Marie back at the makeshift orphanage. Ileum insists that she doesn't need to care for them, but Peacock is too stubborn to give a damn.
There are probably others but I can't think right now, so here you go.