Atsushi Murasakibara is a former member of the legendary Teikō Junior High School basketball club known as the Generation of Miracles and later becomes the center for Yōsen High School's basketball team. He comes from a large family with parents, three older brothers, and one older sister. From a young age, his exceptional height led to him being recruited to play mini-basketball, an opportunity he pursued because it suited his natural physical gifts.

In terms of personality, Murasakibara presents a striking contrast between his intimidating physical presence and his childish, laid-back demeanor. Off the court, he is often described as airheaded, lacking common sense, and having a lazy, unhurried attitude toward most things. He is almost always seen carrying and consuming snacks, with a particular love for sweets such as Pocky and a candy that changes color as it is stirred, and his personal motto is that snacks are justice. He habitually gives nicknames to people he knows, adding chin to the names of friends and teammates, such as Muro-chin for Tatsuya Himuro, and nyan for females, like Satsuki-nyan for Satsuki Momoi. Despite his lazy image, his academic performance is notably strong, ranking third within the Generation of Miracles and achieving sixth place in his grade at Yōsen, with physics being his best subject.

Regarding his motivation and outlook on basketball, Murasakibara famously claims to have little interest in the sport itself, believing that talent is the sole determinant of success and that hard work without natural ability is meaningless. He finds people who love basketball but lack talent irritating, and he particularly dislikes those who cling to the belief of never giving up. This perspective stems from his own experience of dominating opponents through sheer physical prowess, making the game feel effortless and thus boring to him. However, beneath this apathetic exterior lies a fierce competitive nature and a deep hatred of losing. He is also internally cautious about using his full strength because he does not want to hurt others, having set a personal safety line for himself.

Within the story, Murasakibara serves as a formidable opponent, representing the overwhelming physical power that talent alone can achieve. During his time at Teikō, he once scored one hundred points in a single game when provoked. At Yōsen High, he forms one half of the team's dual aces alongside Tatsuya Himuro. His defensive range is so vast that he can cover the entire area inside the three-point line, making him an almost impassable wall. His signature offensive move is a powerful two-handed spinning dunk known as Thor's Hammer, which possesses enough force to break a basketball hoop. He also demonstrates the ability to learn techniques by observation, such as acquiring the Vice Claw, a one-handed rebounding move, after seeing Teppei Kiyoshi perform it.

Key relationships significantly shape his actions and growth. He holds immense respect and a degree of fear for his former captain, Seijūrō Akashi, after being completely defeated by him in a one-on-one match, which also led to Akashi awakening his Emperor Eye. Following this, Murasakibara becomes obedient to Akashi, to the point of skipping an important tournament match simply because Akashi told him not to play. At Yōsen, Himuro acts as another person who can manage him, often using snacks to coax him into activities and delivering a crucial emotional plea that reignites Murasakibara's fighting spirit during a critical match. His relationship with Tetsuya Kuroko is complex and up-and-down; while they get along well off the court, with Kuroko even buying him snacks, their basketball philosophies are direct opposites, leading to frequent arguments about talent versus hard work. Murasakibara also holds a deep disdain for Teppei Kiyoshi, who embodies the persistent, passionate player he claims to hate, and he makes it his goal to crush Kiyoshi during their Winter Cup match.

Murasakibara undergoes notable character development, primarily through his intense match against Seirin High School. Initially, he effortlessly shuts down Seirin's offense. However, when his defense is broken and his team's lead narrows, he becomes enraged and shifts to offense, exhausting Kiyoshi. After Taiga Kagami enters the Zone, Murasakibara becomes demoralized and requests to be taken out of the game. Himuro's tearful anger over wasted talent shames him into continuing, and in the final moments, Murasakibara enters the Zone for the first time, proving that he does harbor a deep passion for basketball despite his claims to the contrary. Following Yōsen's narrow one-point defeat, he tears up in frustration, finally acknowledging his genuine love for the sport. In a later match against the street basketball team Jabberwock, he faces Jason Silver, an opponent who surpasses him in size and strength. For the first time, Murasakibara enjoys the thrill of a challenge, erases his mental safety line, and unleashes his full power before being forced to leave the game due to a broken arm.