Sui, a core member of the Sunset Ravens, begins as an 11-year-old girl housing the soul of her deceased twin brother, Sota. The siblings negotiate control of a single body—Sui’s timid reluctance contrasting Sota’s volatile aggression. Their alternating dominance activates unique Sigils: Sui’s Pollux Light bends water, even within living tissue, while Sota’s Castor Light encases targets in ice. Combined, these powers form devastating combat synergies.

Before joining the clan, Sui shunned violence, grappling with the ethics of survival in their lethal world. Witnessing brutality triggered physical revulsion, yet a mission in Out of Range Village forced her to confront threats directly. Her pivotal role in dismantling the danger signaled a shift from hesitation to resolve, though lingering guilt over fallen allies haunted her progress.

Five years later, 16-year-old Sui retains an androgynous silhouette, her elongated hair and shadowed attire mirroring a hardened demeanor. She now embraces pragmatic ruthlessness, deploying tactics like controlled suffocation or simulated drowning against foes—a stark departure from her past aversion to harm. Speculation swirls around Sota’s true nature: shared soul or fractured psyche? Yet their cooperation endures, blending Sui’s strategic precision with Sota’s ferocity despite clashing morals.

Rooted in the myth of Castor and Pollux, their Sigils echo a bond forged in life and severed by Sota’s unexplained death. Post-timeskip, Sui’s combat prowess and tactical acumen elevate her within the clan, though empathy and remorse temper her newfound lethality, threading vulnerability through her calculated exterior.