i cant really remember many hcs i have that are specific to their relationship, but ill list off a few that i can think of/remember at the moment. might be ooc, feel free to tell me if so:

• i like to think that they all carry around small things reminiscent of & also from the other two: i.e. one of sunday's feathers, one of boothill's bullets, and/or a rose from argenti -they all each have problems with certain aspects of caring for themselves & they all try to encourage & help eachother with it.
• argenti and boothill like to spar, and sunday enjoys watching.
• they all like to cuddle... sometimes sunday will want a blanket inbetween them and boothill because of the metal body and whatnot (sacrifices must sometimes be made for a longer cuddling time, sunday does prefer closer contact but sometimes cannot deal with the discomfort), but argenti never seems to ever even be slightly uncomfortable even if she lies on top of her without her armor on. i think argenti is also a big cuddler, especially when shes sleepy