Aki Hayakawa is best understood as a Self-Preservation Four (SP4), often called the "Tenacity" or "Stoic Four." While many initially associate him with Type One because of his discipline or Type Six because of his loyalty, his deepest motivations consistently align with the psychology of the Self-Preservation Four. His defining characteristic is not simply responsibility or caution, but the quiet endurance of suffering without expecting recognition or sympathy. Rather than expressing emotional pain outwardly, Aki internalizes it and converts it into perseverance, self-control, and duty. The defining trauma of Aki's life is the loss of his family, an event that shapes nearly every decision he makes afterward. Unlike many characters who externalize grief through anger or emotional displays, Aki rarely speaks about his pain. He does not seek comfort, validation, or understanding from others. Instead, he accepts suffering as something that must simply be carried. This attitude closely mirrors the Self-Preservation Four's defense mechanism, which transforms emotional deprivation into resilience. Rather than asking others to acknowledge their wounds, SP4 individuals strive to prove that they can survive them alone. His pursuit of revenge against the Gun Devil is often mistaken for the rigid moral mission of a Type One. However, Aki's revenge is deeply personal rather than ideological. He is not attempting to create a more just society or enforce universal standards. His mission originates from an internal wound that never truly heals. The Gun Devil represents the irreversible loss that defines his identity, making revenge less about justice and more about filling an emotional void that he believes can never disappear. One of the strongest indicators of Self-Preservation Four appears later in the story as Aki gradually develops genuine relationships with Denji and Power. Although he initially treats them as irresponsible coworkers, they slowly become the family he lost years ago. Importantly, Aki never openly admits how much they mean to him. His affection manifests through practical care rather than emotional confession. He cooks for them, cleans after them, worries about their safety, and quietly accepts responsibility for their well-being. This restrained expression of love reflects the SP4 tendency to demonstrate care through consistent action rather than emotional vulnerability. Another defining aspect of Self-Preservation Four is hidden envy. Unlike Social or Sexual Fours, whose envy is often obvious or openly expressed, the Self-Preservation subtype experiences deprivation silently. They perceive that others possess the happiness, security, or belonging they themselves cannot attain, yet they rarely complain about this reality. Aki embodies this pattern remarkably well. As he experiences ordinary moments with Denji and Power, he begins longing for a peaceful life free from devils. Yet he never truly believes that such happiness belongs to him. He appreciates these moments precisely because he assumes they are temporary and destined to disappear. His remarkable self-sacrifice further supports this interpretation. Throughout the series, Aki repeatedly shortens his own lifespan through contracts with increasingly dangerous devils. Although these sacrifices serve practical goals, they also reveal a subconscious belief that his own life carries less value than protecting those around him. Self-Preservation Four frequently accepts suffering as inevitable, viewing endurance as a necessary part of existence. Aki rarely questions these sacrifices because pain has become his normal state rather than an exception. Some may argue that his emotional restraint indicates Type One or Type Six instead. However, emotional suppression alone does not determine Enneagram type. Type One suppresses emotion primarily to preserve moral integrity and maintain self-control according to internal principles. Type Six suppresses fear while seeking security through trusted systems or alliances. Aki's suppression is different. He does not hide emotion because it is morally wrong or because it threatens stability. He hides it because suffering has become deeply personal, something to endure with dignity rather than display publicly. His gradual transformation throughout the story also aligns with SP4 psychology. As he spends more time with Denji and Power, his original obsession with revenge slowly gives way to a desire for ordinary happiness. Rather than dreaming of greatness, status, or victory, Aki ultimately wishes for simple domestic peace. This longing reveals what was always missing from his life: belonging. The tragedy lies in the fact that he only begins to recognize what truly matters after accepting that it may never fully be his. Overall, Aki Hayakawa exemplifies the Self-Preservation Four through his quiet endurance, disciplined response to suffering, hidden longing for an ordinary life, and unwavering dignity in the face of loss. His pain is never theatrical, his affection is expressed through responsibility rather than words, and his identity is built around surviving emotional deprivation without burdening others. Instead of seeking recognition for his suffering, he transforms it into perseverance and self-sacrifice. That combination of silent resilience, internalized grief, and quiet yearning for belonging makes Self-Preservation Four the most compelling Enneagram interpretation for his character.