Shinjiro Aragaki, a third-year Gekkoukan High student, rarely attends class. He co-founded the Specialized Extracurricular Execution Squad (SEES) with Akihiko Sanada and Mitsuru Kirijo in junior high. Shinjiro and Akihiko share a profound bond forged in childhood at the same orphanage, surviving a fire that claimed Akihiko's sister, Miki. Two years before the main events, Shinjiro's Persona, Castor, went berserk during a mission, accidentally killing Ken Amada's mother. Consumed by guilt, he distanced himself from SEES. He began taking Persona Suppressants obtained from the antagonistic group Strega, which caused an inability to regulate body temperature – explaining his constant maroon peacoat and beanie – and gradually damaged his health. Learning of Ken's membership in SEES, Shinjiro rejoins the group, fully aware of Ken's desire for revenge and prepared to face the consequences. In combat, he relies on brute strength, wielding a heavy axe. His Persona Castor specializes in powerful physical attacks like Power Charge, Deathbound, and God's Hand. Though outwardly gruff, aloof, and often perceived as thuggish or intimidating, Shinjiro harbors a kinder side. He demonstrates a genuine love for dogs, spoiling Koromaru with treats and special meals, and is an avid cook who enjoys learning from cooking shows. During the October full moon mission, Shinjiro confronts Ken at the site of his mother's death, intending to submit to the boy's vengeance and warning him that pursuing hatred could lead down a similar path. Their confrontation is interrupted by Strega's Takaya Sakaki, who shoots at Ken. Shinjiro sacrifices himself, taking the bullet. He succumbs to his wounds shortly after SEES arrives. With his final words, he urges Ken to live meaningfully and tells Akihiko to care for him. His death catalyzes Ken's forgiveness and strengthens Akihiko's resolve. Shinjiro's Persona, Castor, symbolizes his tragic connection to Akihiko (whose Persona is the mythological twin, Polydeuces). Castor's instability stems from Shinjiro's unresolved guilt and self-loathing; its berserk episodes reflect a failure to fully reconcile his Shadow self, exacerbated post-accident by his suppressed emotions and reliance on suppressants. In spin-off media like *Persona Q* and *Persona Q2*, Shinjiro maintains his reserved personality but displays a competitive streak, particularly around Akihiko. In *Persona 3 Portable*, the female protagonist can pursue a social link (Moon Arcana) with him, revealing his protective nature and willingness to mentor others. His Linked Episodes in *Persona 3 Reload* allow deeper interactions, including cooking and gardening activities at the dorm. Shinjiro's legacy persists as SEES members hear his voice urging them forward during their final battle. His sacrifice remains a pivotal moment of redemption, emphasizing themes of responsibility and the impact of past trauma on self-acceptance.