Jinta Yadomi, known as "Jintan" in childhood, had black hair and yellowish-brown eyes. He typically wore a watermelon-pink shirt with a circular yellow emblem, dark blue long shorts, and red slippers.

As a child, he was energetic, charismatic, and outgoing. He naturally led the friend group he named the Super Peace Busters, organizing activities and adventures inspired by anime and manga. His peers saw significant potential in him, noting his athleticism and skills like catching large stag beetles. His leadership fostered loyalty and camaraderie, central to the group's shared identity.

He harbored deep romantic feelings for Meiko "Menma" Honma but consistently denied them publicly. When Naruko "Anaru" Anjou questioned him about these feelings, he reacted with embarrassment, impulsively called Menma "ugly," and fled. This denial sent Menma chasing after him, inadvertently causing her fatal accident – an event that profoundly shaped his later life.

He formed the Super Peace Busters with the idealistic goal of maintaining neighborhood peace, reflecting his childhood optimism and sense of responsibility. His refusal to admit his feelings stemmed from youthful insecurity, a decision that haunted him and contributed to the group's fragmentation. The trauma of Menma’s death and his unresolved guilt over his role catalyzed his withdrawal from society as a teenager.

Later reflections underscore how his childhood actions and the unresolved guilt surrounding Menma’s death influenced his relationships and personal growth into adolescence and adulthood.

A notable physical trait was his left-handedness, evident in his use of utensils and writing. The name "Jinta" combines the characters for "benevolence" (仁) and "thick/big" (太), reflecting traits defining his childhood persona.