TV-Series
Description
Tsukushi Tsutsukakushi, the older sister of Tsukiko Tsutsukakushi, possesses sapphire-like eyes and long dark hair usually tied back. Her tall stature and notable physical development contrast sharply with her sister's petite frame. She is frequently seen in her track and field uniform.

Following the early deaths of both parents, a typhoon led to Tsukushi and Tsukiko being sent to live with grandparents in Italy, while their mother, Tsukasa, remained in Japan due to poor health. Years later, during a failed reunion attempt in Japan, Tsukushi expressed anger at her mother's absence by throwing pebbles, one accidentally injuring Tsukasa. This incident prompted the younger Youto Yokodera to sacrifice his memories of Tsukasa to the Cat God, transferring them to Tsukushi so she could experience cherished moments with her mother. This sacrifice caused Youto's lifelong inability to retain long-term memories.

As a teenager, Tsukushi rose to become president of the track and field club, earning the moniker "Steel King" for her disciplined leadership. Her profound protectiveness towards Tsukiko evolved into intense romantic feelings. She formulated a plan to study in Massachusetts—where same-sex marriage is legal—intending to sever their sisterly bond to marry Tsukiko, causing Tsukiko significant distress. During an argument with Tsukiko, she prayed to the Cat God for reconciliation and received wood and carving tools. She used these to create the Stony Cat statue as an apology gift, an object that later became central to supernatural events.

Tsukushi initially admired Youto for his apparent dedication to the track club, unaware it was a facade for voyeuristic intentions. She appointed him as her successor. His subsequent erratic behavior, resulting from wishing away his "façade" at the Stony Cat, led her to misinterpret his actions as stress-related. Witnessing Youto and Tsukiko together ignited jealousy, prompting a confrontation where Youto fabricated a story about an "evil twin brother." Believing this lie, Tsukushi developed separate feelings for the "twin" and even planned to assassinate him to protect Tsukiko. She later proposed moving to a polygamy-friendly country so the "twin" could marry both her and Tsukiko.

Her relationship with Tsukiko is deeply affectionate yet complicated. She obsessively documented Tsukiko through photos and videos, including private moments, to preserve her "cuteness," acknowledging this behavior might be overwhelming. Mai Maimaki, the track club's vice president, idolized Tsukushi with near-religious devotion, desiring physical and emotional closeness though hesitant to express it openly.

A latent "curse," stemming from Tsukasa's adopted belief as a coping mechanism for her illness, manifested years later in Tsukushi, causing severe health deterioration. Youto sacrificed his remaining lifespan to the Cat God to save her, triggering a time loop where Tsukiko repeatedly relived the events. Ultimately, the curse's origin was traced to Tsukasa's wish during her loneliness, which inadvertently separated Youto from his biological family. A second time leap nullified both this wish and Tsukushi's inadvertent wish expressing love for her mother, creating a new timeline where the curse never existed.

In this revised timeline, Tsukushi's obsession with Tsukiko and the "curse" were erased, though her core personality and role as track club president remained. Her interactions with Youto reset, though Tsukiko's retained memories eventually helped reestablish their connections.