[DrChief]

I actually read somewhere on a Tumble post (yes, that site, please forgive the transgression) that Vice's contradictory actions makes sense if seen as the actions of an impulsive child, and I can kind of see that. He has that feel of the annoying younger brother who gets on your nerves, but push comes to shove, and it's shown that he does care in some way.

Remember that the Demons tend to represent a part of the humans themselves, whether it be Lovekov embodying Sakura's weakness or Kagerou embodying Daiji's resentment.

Going by that logic, Vice isn't just necessarily Ikki's resentment towards his family, but rather his sense of childhood. Okay, I'm probably rambling at this time, but I could kind of see this line of logic since Ikki does appear to act like a parental figure to his siblings, which I think stands out since Genta is not exactly the most, well, "dutiful" parent as of now. Yukimi is better but considering that she doesn't seem to notice the problems Daiji and Sakura have while Ikki immediately notices... Eeeeeh.

This could explain why Vice moves to attack Ikki's mom when Vice first manifested: Vice was acting on Ikki's suppressed emotions at the time, and while grateful to his mom, Ikki may have wanted her to become more involved with his siblings, and felt some resentment that she didn't.