I bet Vanitas is like. the most indirect kind of supportive to the people he cares about. he can't LET THEM know he cares. so it's all fueled by rage
he gets pissed on Sora's behalf so that he understands that someone will be angry for him, even when Sora thinks he isn't allowed to be upset. he'll be honest to the point of cruelty in hopes that he can validate the fears that Sora won't say out loud. but every time Sora thanks him, Vanitas just insists it's because he's so angry he can't resist
with Roxas they are angry in tandem, furious at the world that'd bring them into existence and then treat them the way they have. the world is so cruel to boys so artificial and if they were so forcibly brought into this world, don't they deserve some kindness for once? it's easier for Vanitas because Roxas understands, intuitively, what his support looks like. he dares not get mushy - he knows sparring to blow off steam is thanks enough
but sometimes anger is too ancient and close to home. sometimes he stands with Ventus and he doesn't really know what to do with his hands. Ven wants to talk but Vanitas still isn't great at listening, so he sits on the floor legs crossed like a child and Ven hands him stim toys and art supplies and cardboard that he can tear into shreds with his hands because Ven knows that Vanitas's feelings are too big for his body and he could use some help figuring out what to do with them
