SIRIUS often described as emotionless, quiet but not shy — and blunt. He was lacking the skill of expressing his emotions or expression, caused by the pressure to look okay or dependable to his siblings when things went down with their parents. It was something that he carried through from when he was child to an adult.

By that, Sirius also tends to care more for wellbeing of people he decided really mattered to himself. He was loyal, but he wouldn't give too much fuck for others than them. He's also a bit of pathological liar, mostly involved what he's feeling currently.