Itsuki is a 17-year-old rapper with 1Nm8, defined by an emotionless demeanor and a rationalist outlook. This behavior originated when he became a test subject for Alter Trigger Corporation's phantometal experiments at age five. Those trials granted him "Shutter Eye," a superhuman memory that traps every detail, especially traumatic or painful recollections, preventing him from forgetting anything. To defend against the overwhelming vividness of these constant memories, he suppresses his emotions. This perfect recall also makes him prone to holding grudges. Physically, he possesses short black hair streaked with light grey strands at his fringe and bright yellow eyes. His signature attire includes a white blazer featuring diamond buttons and sleeves patterned with barcodes, white pants displaying front splits, and black laceless shoes. He wears lenseless wire-frame glasses with a chain. Multiple tattoos mark his body: a geometric square phantometal design on his right hand extending up his arm, zigzag and double helix patterns on his wrists, and a neck tattoo of chevrons pointing to a central geometric shape. A ring adorns his right middle finger, and he has a piercing in his right ear. His daily life emphasizes efficiency and control, structured into strict hourly intervals. Activities encompass household chores, grocery shopping, meal preparation, and scheduled walks with Kei and Rokuta. He prioritizes Rokuta's care, allocating specific times for snacks, video gaming sessions (played until Rokuta wins), and supervision. Reading and decluttering are his hobbies, with baking soda noted as a favored household item for its utility. He avoids illogical statements, shows a preference for spicy food, and dislikes liver. Relationships are few but significant. He shares a home with Kei (1Nm8's leader and former VISTY idol) and Rokuta (a fellow test subject). Despite emotional restraint, he exhibits protective instincts toward Rokuta, who calls him "Big Brother Itsuki" (イツキ兄). Their bond formed at age ten as roommates in Alter Trigger's facility. Itsuki manages most domestic responsibilities in their household, demonstrating pragmatic care. He refers to Kei by name without formalities, suggesting mutual reliance despite Kei's leadership role. His phantometal, the Geometric Square Tattoo (ジオメトリカルスクエアタトゥー), activates when he kisses the tattoo on his right hand. The experiments that bestowed Shutter Eye inflicted lasting psychological trauma, encapsulated in hashtags like #MemoriesOfVividPain, #CantForgetAnything, and #DriedTears. These experiences shape his worldview, leading him to question the fundamental purpose of emotions like "smiles and tears."