1, 3, and 7 for the milgram oc asks if you want :D
I don’t personally have OCs for Milgram so I will be using my already existing OCs for this.
For one, I would have to say that Mei would get along with Haruka in both trials same with Ai aside from AI (the other parts of herself/kind of her alters the story she’s from does deal with magic but her condition is very similar to DID) and would be besties with Muu in trial one but would grow to have resentment for her and tried to warn Haruka about her to no avail and get him to not sacrifice himself for her to no avail as well in trial two despite initially liking Muu’s boost in self-confidence (Ai and AI would hate her from the start.) I also think she would get along well with Mahiru despite getting overwhelmed constantly around her due to Mahiru being Mahiru. Honestly I can imagine Mei and the rest of her system getting along with mostly everybody despite Ai and AI’s more reserved and un trusting and rightfully defensive personalities and attitudes and AI’s general dislike of humans despite wanting to connect with them and the other members of her system (Ai is besties with Yuno, Shidou, Kazui, and Mikoto and John! While AI is pretty much besties with John and Kotoko) aside from Fuuta! They all collectively hate him. It’s literally the one thing they can agree about is that this man needs to die a violent and painful death!
And for 3, they are making whoever comes in contact with them worse no matter what! Muu, Haruka, Fuuta, Mahiru, Mikoto and John, and Kotoko are made so much worse because of Mei and AI’s terrible advice and encouragement of their worst actions because of their own twisted view of how the world works and their own trauma and Fuuta is made worse because mental torture and bullying he suffers from them especially from Ai who hates him specifically because she see herself in him and hates the fact that he believes he deserves to be saved and that he can be saved. However AI does encourage Kotoko to be less ableist towards Mikoto and John and also tries to make her understand that she in a way is similar to John and encourages him and her to work together to no avail.
Their symbols are pretty similar to Haruka and Mikoto (sorry do not fully understand the seventh question).











