Black Star (ブラック☆スター Burakku Sutā, stylized as "Black☆Star") is a assassin and the meister of Tsubaki. He is exceedingly arrogant and loud-mouthed for an assassin, preferring to make a flashy entrance rather than sneaking up on his opponents, and tries to upstage anyone who gains more attention than he does.[] He frequently calls himself a "big" man destined to surpass God, thus driving himself to his physical limits and making him one of the most athletic students at DWMA. He made it a personal goal to defeat Kid in battle since Kid is a 'death god'. He is a skilled combatant even when unarmed, using a skill that allows him to increase his own soul wavelength and channel it through physical attacks.[] He is one of the last remaining survivors of the Star Clan, a family of ninja assassins who slaughtered others for wealth until they were wiped out by DWMA, which took him in as an infant. He is oppressed by anyone who recognizes the clan's symbol, a star-shaped tattoo on his shoulder.[] Due to his obsession with power and to the fact that the Star Clan was wiped out because they started to consume souls, some believe he will eventually descend down the path towards becoming a kishin like his father White Star.[] But, in the final battle with Minfune, he chooses not the path of the Demon, but not the Warrior. He chooses the path of his own. Black Star, in his introductory chapter, is shown to have an attraction to Tsubaki, as he tried twice to peep on her while bathing; the feeling seems mutual as in the Lust chapter of Eibon's book, Tsubaki takes a form similar to Black Star when everyone's gender is switched.

In the anime, Black Star tends to have differences with both Maka and Kid. Maka had a hard time completing Soul Resonance with him because he was so arrogant and self-centered during Stein's training to make him, Maka, and Kid a team. Maka even punched him out of frustration towards his insults at her of her being weaker than him. Kid sometimes got into physical fights with Black Star, such as when Black Star would mess up 'perfect' symmetrical objects.