Ryuji Sakamoto, a student at Shujin Academy, emerges from a troubled home life marked by an alcoholic father who physically abused him and his mother before abandoning them. This fuels Ryuji's deep resentment toward corrupt authority and fierce protectiveness of his mother, his only family. He co-founds the Phantom Thieves of Hearts, adopting the codename "Skull."

Once the trusted leader of Shujin's prominent track team, Ryuji's athletic career ended when teacher Suguru Kamoshida, seeking volleyball team dominance, intentionally injured Ryuji's leg during a confrontation. The incident led to the team's disbandment and Ryuji being branded a "traitor" by peers. The injury caused a permanent limp, causing occasional trips if he overexerts himself.

Beneath a rebellious delinquent persona lies a complex character: energetic, fiercely loyal, and committed to justice, yet struggling with impulsivity and a short temper. Kamoshida's abuse solidifies his resolve to fight injustice, driving him to awaken his Persona, Captain Kidd (later evolving into Seiten Taisei), and form the Phantom Thieves. His core motivation is protecting others from similar trauma, compelling him to advocate continuing the group's activities after Shiho Suzui's suicide attempt and encounters with politician Masayoshi Shido.

Ryuji's journey involves overcoming his past and redefining his identity. He reconciles with resentful former track teammates, demonstrating forgiveness and urging them to confront their new coach's corruption. Confidant interactions see him progress from guilt and self-doubt to acceptance, culminating in declining a track team reinstatement offer; he finds his true belonging with the Phantom Thieves, stating his desire to "focus on being free."

As a frontline combatant, Ryuji specializes in powerful physical attacks and electric skills. His tactical abilities include follow-up strikes, curing party status ailments, enduring lethal blows, and shielding teammates. A later skill allows instantly defeating weaker enemies, expediting exploration. His Persona's evolution to Seiten Taisei nullifies electricity and improves wind attack evasion.

Ryuji sports short, spiky dyed-blond hair (naturally black), dark brown eyes, and a muscular build. His civilian style reflects rebellion through graphic tees, cargo shorts, and sneakers. His Phantom Thief attire features a skull mask, a black jacket with a metallic vertebral spine, combat boots bearing a Rising Sun Flag motif linking him to the "yankii" subculture, and a red ascot.

Within the Phantom Thieves, Ryuji acts as charge commander and shares a close bond with the leader. His arc concludes with him fully embracing his role, declaring the team his true place to belong.