Asta is a young man of short stature with a muscular build. He has green eyes and messy ash blond hair with a single strand protruding upwards from the center of his head. He keeps his hair together with a black headband, which has the gold-colored Black Bull insignia and has a red-colored four-sided star with three stitches on the back of it.
Asta's common outfit consists of a plain-white tunic with a V-shaped collar underneath a dark blue jacket whose sleeves extend only up to his elbows. He sports a pair of matching shorts which has a stitch marks on the left side. His pants also extends just below his knees. His shoes is made out of two different cloths, the parts covering his ankles, the soles the same color as his jacket and pants. The parts covering his toes are white, a vertical stitch mark going from the bridge to his toes. When he's sending his anti-magic in his body, it surrounds the right part of his body with black matter and he gains a partial demon transformation.
After receiving his grimoire, Asta wears a pouch strapped to a brown leather belt. Additionally, as a member of Black Bull, he wears his squad's signature robe, which is black and short with gold trimming and covers the upper half of his torso. It also has a hood and a gold-colored button located at the right-hand side to hold it together, while the left-hand side displays the squad's insignia.
Asta's explosive nature.
Asta generally is cheerful and hyperactive. He tends to shout to express his thoughts and expresses his goals, regardless of other people's opinions, as seen when he expressed his goal on becoming a Magic Emperor during the Magic Knights entrance exam, where he tells other people who disagree with him to be quiet. His strong tenacity interests Yami Sukehiro enough to recruit him into his ranks. His strong determination also leads him to have a strong will to never give up and keep standing during a harsh battle, as acknowledged by Magna Swing.
Because of his upbringing at the Forsaken region, Asta frequently receives harsh opinions and insults from almost everyone he meets. This makes Asta have a slightly sarcastic nature as he tries to defend himself. But, having received harsh opinions from others, Asta has developed an immunity to them as he could easily brush them off without getting overly annoyed. However, Asta is still annoyed when others deeply insult his comrades; he will not hesitate to confront them as he tries to defend his friends.
Asta accepts Noelle as his comrade.
Asta also has a very strong sense of justice, which is shown during his fight against Heath Grice, as he believes that everyone deserves to be protected. It is also not limited to only his comrades but his enemies as well, as noted when he asks his fellow squadmates to take the unconscious Mars along with them while the dungeon is collapsing. He argues that their mission is only to explore a dungeon as they are not ordered to kill any enemies. Therefore, Asta seems to see the positive side of everyone and never takes an insult too seriously, as seen when he still befriends both Yuno and Noelle Silva even after both given him harsh opinions.