Mitsuba Sousuke exists as two distinct entities sharing common origins. The original Mitsuba was a human student in Kamome Academy's middle school division. He possessed pink hair, androgynous features with a mole under his left eye, and typically wore a pink cardigan over his uniform paired with a distinctive yellow scarf featuring brown and blue stripes. His personality shifted dramatically due to bullying; once cocky, foul-mouthed, and confident about his looks, he adopted a passive, polite facade in middle school to avoid harassment. This strategy failed, leaving him largely forgotten by classmates. He cultivated a deep passion for photography, often focusing on nature and animals rather than people, and won awards for his work. His life ended in a winter accident while rushing to buy potatoes for his mother's birthday curry. After death, the original Mitsuba manifested as a low-level supernatural haunting school lockers. Visible only when grabbing someone's hand, he desperately sought recognition from former classmates. Yugi Tsukasa forcibly transformed him into the violent "Broken Neck" entity – a form composed of eyes and camera parts bound by bandages, lacking verbal communication or human awareness. Hanako destroyed this entity to end its suffering. A recreated Mitsuba emerged when Tsukasa fused fragments of the original's soul with component supernaturals. This entity consumed the heart of the former School Mystery No. 3, becoming the new representative of the Hell of Mirrors. Visually distinct from the original, he wears a red scarf with five tassels and golden trinkets, including a "三" (three) kanji tag. As No. 3, his appearance features a tattered black jacket adorned with eyes, black feathers in his hair, and a bird-like talon for his right hand. His scarf extends into bony exoskeletons that function as appendages. Personality traits persist across both versions: loud self-confidence about his appearance, sarcasm, and the use of insulting nicknames mask profound loneliness and insecurity. The recreated Mitsuba exhibits jealousy toward his original self and grapples with identity, rejecting the name "Sousuke" introduced during the Picture Perfect arc where he impersonated the human Mitsuba. He typically introduces himself solely as "Mitsuba," reflecting his fragmented sense of self. His core desire remains unchanged—to be remembered—though he expresses it through aggression or manipulation. Abilities evolved with each form. As a locker ghost, he could manifest partially to humans. The Broken Neck entity attacked with bandages. As No. 3, he commands the Hell of Mirrors boundary, accesses reflections for information retrieval, and controls his exoskeleton scarf as weaponized limbs. Emotional distress triggers involuntary attacks from these appendages. Significant details include his favorite snack (flan pudding), concern about his inability to build muscle, and fear of lightning as a human. The recreated Mitsuba finds Tsukasa more frightening than lightning. His name "三葉" (three leaves) foreshadows his role as the third School Mystery, while "惣助" (Sousuke), meaning "whole," contrasts with his fragmented existence post-recreation.