He also has noticeably thick dark eyebrows, and has always been having a soft yet menacing smile plastered on his face nearly at all times, even when injured by Akaza. It looks like Doma had the same blue nails when he was still Upper Rank Six, but the only difference is that it was blunt, short and therefore not sharp. Once he became Upper Rank Two, they seem to have became sharp and more claw-like, or it could be his claws are retractable, like Muzan Kibutsuji himself.