Atsumu Matsuyuki, universally known by his childhood nickname Yukiatsu, stands as a central figure within the friend group called the Super Peace Busters. As a child, he possessed a quieter and more serious demeanor compared to the energetic leader, Jinta Yadomi, and was often perceived as somewhat cowardly. This early dynamic fostered an underlying inferiority complex towards Jinta, persisting despite Yukiatsu's outward success later in life. Physically tall and slim, he stands approximately 180–181 cm (5'11") and weighs 68 kg (150 lbs), with light brown hair and green eyes. During his teenage years, he typically wears his school uniform: a white collared shirt, dark blue jeans, a burgundy tie, and brown shoes, often accessorized with a wristwatch featuring a brown leather strap. His childhood attire included a distinctive blue and yellow cap with a fish emblem, a buttoned shirt, denim shorts, calf socks, and orange-and-white running shoes. The accidental death of their friend Meiko "Menma" Honma during childhood left Yukiatsu deeply tormented by guilt and grief. He specifically blamed himself, believing his confession of feelings to her that day caused the tragedy. This unresolved trauma fueled increasingly complex and harmful behaviors in his teenage years. Though academically successful at an elite high school and outwardly projecting confidence, intelligence, and athleticism, he often adopted a condescending, arrogant, and hostile attitude, particularly directed at Jinta. This facade masked intense vulnerability and profound emotional pain. His grief manifested in extreme actions. He secretly obtained and kept a white sundress identical to the one Menma wore when she died. Consumed by jealousy when Jinta claimed to see Menma's spirit and desperate to feel close to her, Yukiatsu began wearing the dress and a wig at night, imitating Menma and wandering the forest where she died. He initially claimed he could also see her ghost, but this was revealed as his own cross-dressing charade. Discovered by his friends, he confessed this behavior stemmed from a desire to embody Menma and a conviction that he, not Jinta, deserved to be haunted by her ghost due to his perceived culpability. Though he ceased the cross-dressing after being caught, his anguish and obsession endured. Yukiatsu recognized a kinship with Naruko "Anaru" Anjo, confiding in her about their shared experiences of unrequited love – his for Menma and hers for Jinta. He acknowledged that both were "left behind" by these feelings. Despite this moment of connection, his manipulative tendencies, driven by unresolved emotions and his inferiority complex towards Jinta, frequently surfaced. He actively undermined Jinta's claims about seeing Menma and sabotaged efforts to grant her supposed wish, motivated partly by resentment and partly by a fear that fulfilling the wish would sever his last connection to Menma. His development involved a gradual, painful acceptance. He eventually acknowledged the reality of Menma's ghostly presence and joined the reunited Super Peace Busters in their efforts to help her pass on. During this process, long-suppressed emotions erupted, leading to intense arguments where hidden vulnerabilities and resentments within the entire group surfaced. Yukiatsu confronted Jinta's perceived selfishness in clinging to the past, accusing him of hurting everyone, including Menma's parents, by being "chained down" by her memory. This harsh confrontation forced a collective catharsis. A pivotal moment occurred when Yukiatsu demonstrated a willingness to humble himself completely for Menma's sake, getting down on his hands and knees to beg during a failed attempt to help her move on. Ultimately, resolution arrived with the revelation of Menma's final letters to each friend. Her letter to Yukiatsu explicitly acknowledged his core traits, stating, "I love how hardworking and strong you are." Receiving this message and participating in the group's collective farewell to Menma enabled Yukiatsu to begin releasing his guilt and anguish. By the series' conclusion, he showed signs of moving forward, notably growing closer to Chiriko "Tsuruko" Tsurumi, hinting at a healthier emotional future.