Tadayoshi Tōyama, nicknamed "Soldier" for his military ambitions, was incarcerated in the Shōnan Special Reformatory after violently attacking his mother's abusive lover and inflicting severe injuries. His imposing physique and distinctive facial scars created an intimidating presence, masking an underlying principled nature.

Initially distrustful of fellow inmate Rokurouta Sakuragi, he challenged him but was overpowered due to Sakuragi's boxing skill. This defeat fostered mutual respect, leading Tōyama to integrate into the Cell 6 group. He maintained a rigorous self-imposed training regimen, steadfastly viewing military service as his future. His physical strength and fierce loyalty drove him to repeatedly defend cellmates against guard and inmate brutality, enduring severe punishments to protect others.

Upon release, he enlisted in the Japan Self-Defense Forces, achieving his ambition. His military career halted when he voluntarily confessed to crimes committed by a foreign criminal organization to shield Mario Minakami from prosecution, resulting in his re-imprisonment. After Ryuuji Nomoto pursued legal avenues to reduce his sentence, Tōyama secured release.

He transitioned to a role as a reformatory guard, focusing on providing emotional support and rehabilitation guidance to inmates, informed by his own experiences. Personally, he married Meg Yokosuka, started a family, and achieved stability. His enduring commitment to friendship was demonstrated by his participation, alongside former cellmates, in fulfilling a promise made to Sakuragi.