Kazuna Kouzuki, twin sister of Yura Kouzuki, stands as a pivotal force within the narrative. Born into the Kouzuki family yet reared apart from Yura, she remains oblivious to her twin’s suffering under their father Keiichiro’s cruel regime of familial ostracism and exploitation—a stark contrast to Yura’s traumatic reality of being sold as a test subject and manipulated by figures like Detective Arishima. Kazuna’s sheltered existence clashes sharply with her sister’s harrowing past.

Driven by determination and compassion, she allies with Shugo Takashiro to uncover Yura’s mysterious disappearance, a quest intertwining with the Ueno serial mutilation murders and the shadowy cult Senri’s corrupt hierarchy. As their partnership deepens through shared trials, Kazuna’s naivety toward Yura’s psychological unraveling emerges as a critical narrative tension.

The True Ending reveals her resilience amidst cascading tragedies. After enduring the deaths of Rin, Takako, and Tokiko, Kazuna pursues acting abroad, striving to inspire her comatose sister despite Yura’s calculated violence to isolate Shugo. Her return in the fandisc after-story as a renowned actress reunites her with Shugo and Toji, but Yura’s resurgence triggers a fatal clash—ending with Toji killing Yura to protect Kazuna. This finale cements Kazuna’s role as an anchor of stability against familial and societal collapse.

Her journey grapples with identity and legacy, juxtaposed against Yura’s vengeance-fueled actions born from abuse. While Yura’s choices spiral from manipulation and trauma, Kazuna’s path underscores tenacity and moral clarity, even as she confronts the fallout of her sister’s decisions. Positioned as both survivor and catalyst, she bridges the fractured Kouzuki lineage, seeking closure amid enduring shadows of the past.