Tamaki Yotsuba endured a harsh childhood marked by an abusive alcoholic father. His mother brought fleeting joy by sharing King Pudding with him and his younger sister, Aya. After her early death and his father's disappearance, Tamaki and Aya entered an orphanage when he was approximately three. Aya’s adoption by a mid-sized company president separated them, though they maintained correspondence until her adoptive family vanished during bankruptcy. This instability fostered Tamaki’s abandonment issues and subconscious distrust of adults, driving him to exploit others preemptively. He remained in the orphanage for roughly fourteen years until late adolescence.

Scouted by Otoharu Takanashi while street-dancing for coins, Tamaki accepted Otoharu’s proposal upon learning it involved television appearances—a potential path to finding Aya. He joined Takanashi Productions after bargaining for spaghetti, confident he could overpower Otoharu if betrayed. This quest fueled his initial idol career.

Tamaki possesses light blue shaggy hair, typically loose but occasionally tied in small ponytails or braids for performances. With blue eyes and standing as IDOLiSH7’s tallest member, his personality blends emotional sensitivity with a gruff exterior. He intuitively detects others’ emotions and reacts intensely to anger or deceit, often becoming distressed. Despite impulsiveness, tardiness, and a habit of addressing superiors with casual nicknames—sometimes causing friction—he remains inherently kind-hearted. He avoids overanalysis and moves at his own rhythm. Childhood nostalgia fuels his fierce love for King Pudding and budget snacks; he despises food theft. His interests include gacha-based video games, card-strengthening mechanics, manga, and shonen anime featuring power-ups. He knows constellations and yearns to stargaze with companions. He lacked a mobile phone until scouted.

In IDOLiSH7, he partners with Sogo Osaka in subunit MEZZO". Their dynamic is contentious: Tamaki’s laxity clashes with Sogo’s strictness, and Sogo’s reprimands trigger Tamaki’s anger sensitivity. Yet their bond evolves; Tamaki grows to value Sogo’s gestures, like arranging a King Pudding Museum trip for his birthday. He shares a playful rapport with classmate Iori Izumi, once pitching a "Buff Body Builder" role for him. As anime-watching buddies, he and Nagi Rokuya cry openly during emotional scenes. Tamaki shows protectiveness, carrying exhausted Riku Nanase post-concerts or fetching out-of-reach items for him.

His development focuses on conquering trust issues. Early on, he resisted relying on adults, deeming their support temporary. A turning point came during solo overexertion on a filming project to prove independence to Sogo. Hesitating to seek aid from manager Tsumugi Takanashi—a rare consistent adult ally—revealed his fear of vulnerability, signaling newfound faith in IDOLiSH7’s permanence. At his King Pudding Museum birthday, he initially wished his mother and Aya attended but chose to share limited-edition pudding with Yamato and Sogo, who dislike sweets. Prioritizing their company over his craving, he hoped this act improved their experience, showcasing empathy. The group pledged a future group visit, cementing his belonging.

Additional traits include peak physical stamina, ranking him IDOLiSH7’s strongest. He connects easily with children, understanding their worldview. Witnessing Riku drunk solidified his alcohol aversion. Humorous mishaps involve causing a bug infestation via abandoned pudding cups and losing solely the backstroke race to Iori by veering off-course.