Sanae Dekomori, a third-year junior high student, cultivates an eccentric persona tied to chūnibyō delusions, forging a close alliance with Rikka Takanashi through shared fantastical roleplay. She sports long blonde twintails anchored by weighted pouches dubbed "Mighty Mjolnir Maul," theatrically claimed to induce mortality in adversaries. Originally stuffed with candy and cookies—later deemed impractical—these accessories underscore her whimsicality. Academically adept, she masters middle school mathematics early and tackles advanced problems effortlessly, earning peer admiration despite her oddities. Her self-styled role as Rikka’s devoted "servant" originates from online exchanges predating their real-world meeting, where she investigated parallel worlds under aliases like "Tyrant’s Eye" and "Mori Summer." She staunchly disputes Shinka Nibutani’s claim to the latter identity, branding her an impostor. Her speech merges formal diction with playful distortions, punctuating sentences with "-desu" as a nod to "death," reinforcing her fantastical affectations. Though immersed in roleplay, she intermittently acknowledges the artifice of her delusions. Hailing from affluence, her background includes chauffeur-driven arrivals with attendants. Narrative progression sees her elected class representative and later student council president in high school, roles demanding negotiation between duty and fantasy. One arc pits her against institutional authority when tasked with monitoring Rikka and Yuuta, testing her loyalties. Her rivalry with Shinka oscillates between physical clashes and barbed exchanges, occasionally revealing mutual concern. A supplemental storyline adds nuance through an accidental first kiss during a comedic blunder. Collaborative delusions with Rikka escalate in side narratives like the "Depth of Field" specials, where imagined mecha battles coexist with academic diligence. Persistent quirks include dairy aversion—she reluctantly drinks milk to spur growth—and susceptibility to motion sickness. Her wardrobe juxtaposes modified school uniforms with frilly, childlike elements, mirroring her struggle to reconcile adolescence with lingering juvenility.