Black Star is a young boy of Japanese descent and is twelve to thirteen years of age. He has bright blue spiky hair, with the spikes sticking in out in the manner of a star-shape. He is rather short, not that much taller than Maka, but has a well-muscled build due to constant training. His eyes are green and when under the effects of madness, his eyes adopt star shaped pupils, which is seemingly a distinct trait of those belonging to the Clan of the Star. His main outfit is a sleeveless black shirt with a funnel-like collar, with white trousers that are black from the knee down and just a little short of being full length jeans. On the front of his collar, two short strips of grey material adorned with rivets stretch down fro, the top of the collar to the breast of his shirt. Black Star has similar strips wrapped around his neck in the form of a scarf, and around his waist in the form of a belt. Rivets can also be seen on his pockets and on the ends of his trousers. On his hand, he wears gray fingerless gloves with heavy wrist weights and has a band going across the back of each hand, adorned with a star. Black Star's footwear are basic black boots with white tips, with a star shape visible on the toe of each boot.
On his right shoulder is his star-shaped tattoo, showing his heritage as a member of the Star Clan which is just a shade lighter than his normal skin tone. In earlier concept art, this tattoo had a more complex design with black markings and a symbol in the centre.
As of joining Spartoi, Black Star now wears blue pants with the hemline rolled a few inches above his ankles, with white shoes and a white belt that is similar to an obi. His feet are wrapped in bandages up to his ankles and his hands and arms are also wrapped in bandages up to the elbow. As per his previous attire, Black Star wears a sleeveless top. In this case, it is a custom, white, muscle shirt. Another new addition is a long white scarf, wrapped around his neck with the majority hanged loosely. He also has a fairly noticeable scar running across his tattoo on his right deltoids, numerous smaller scars scattered across his arms, and a faint scar-line running down his right eye—all of which were caused by Mifune during their last match. The spikes in his hair are a lot messier and not as star-shaped. Black Star has also grown in height, almost equaling his partner, Tsubaki.
His soul is bright blue, and has numerous sliks coming out of it in the manner of his hairstyle. When Resonating with Tsubaki, various black tattoos appear around it.
In the Chapter of Lust in Eibon's Book, he is transformed into a girl. His build becomes similar to Tsubaki's, although his attire is still the same, apart from the fact that his trousers turn from blue to white. His hair becomes slightly shorter and no longer spiky, taking on a more feminine look. He is also well-endowed (a fact that he does not hesitate to declare incredibly loudly to his friends).