Hikari Myodo is a central figure in the narrative, primarily defined by her role as the younger sister of the protagonist, Akina Myodo. Her existence is profoundly shaped by an incident from ten years before the main story, when she wandered into ruins during a summer camp and became the unwilling host of an otherworldly entity named Sybilt. This possession manifested as a chronic, debilitating illness that has led to frequent and lengthy hospitalizations throughout her childhood, a condition that has also slightly stunted her physical growth compared to her peers. Despite this frail constitution, Hikari generally presents a bubbly, cheerful, and easily excitable personality, maintaining a positive attitude and teasing her devoted brother, showcasing a strong and resilient spirit. She is a passionate fan of Cardfight Vanguard, often playing and adjusting her deck while in the hospital, and is moved to tears by the intensity of professional matches.

However, this external brightness conceals a deep well of guilt and regret. Internally, Hikari blames herself for the summer camp accident, believing that her illness has effectively stolen both her and her brother’s childhoods. She feels immense remorse that Akina has had to sacrifice his own dreams and free time to care for her, a burden she wishes she could lift from him. This profound desire to undo her past mistakes and rewrite history becomes her primary driving motivation, creating a deep-seated wish to travel back in time to prevent the original incident. This guilt and self-loathing are so potent that they resonate with the entity Sybilt and the spiritual being Liael, who shares similar regrets and possesses power over time.

Hikari’s role in the story is uniquely complex, involving two distinct versions of herself from diverging timelines. In the original timeline, Akina lost the Fated Clash tournament, a wish-granting competition he entered to cure Hikari, resulting in his death. Three years later, a traumatized, cynical, and hardened future Hikari won the next Fated Clash. Using her wish, she traveled back in time, donning a fox mask to conceal her identity, to force Akina to forfeit the tournament and save his life, fully aware that this act would erase her own timeline. This future Hikari is cold and distant, driven by desperation, and willing to manipulate other participants to achieve her goal. Conversely, in the current timeline where Akina succeeds and cures her illness, the present Hikari becomes corrupted by Sybilt. This corruption magnifies her existing guilt into bitterness and coldness towards Akina, leading her to join the Destined Showdown with the same goal of time-traveling to prevent her original possession.

Her most significant relationship is with her brother, Akina, which is a tapestry of love, guilt, and conflict. She deeply loves him but is also his most vocal critic, believing his overprotectiveness and self-sacrificing nature are a direct result of the burden she has placed on him. In her corrupted state, she actively avoids him and confronts him as an opponent, claiming that changing the past is the only way to restore his sense of self-worth. Her relationship with herself is also a key point of development, as the future and present Hikari eventually clash. During this confrontation, the more mature future Hikari challenges her present self’s motivations, arguing that her desire to change the past is selfish and ignores Akina’s own choices and the joy he found in caring for her. This defeat breaks Sybilt’s mental corruption and forces the present Hikari to reconcile with her brother, accepting his agency and agreeing to support each other mutually.

Her development is a journey from passive sufferer to active agent, albeit one often misguided by self-destructive guilt. The future Hikari learns to trust her brother, acknowledging that her intervention changed the timeline enough for him to succeed. She ultimately fades from existence after her paradox is resolved, though in a final turn of events, she is saved from erasure and chooses to remain in the current world as a new individual, taking the name Erica. The present Hikari, after her defeat, learns to accept her brother’s decisions and let go of her self-perception as a sinner. In combat, Hikari is a formidable fighter, having won a Fated Clash in her own future timeline. Her notable abilities are intrinsically linked to her Avatar unit, Liael, which exists in two forms. As the future Hikari, she uses Liael=Amorta, a unit from Keter Sanctuary whose power involves rewinding time to give units an additional chance to attack, symbolizing her desire to rewrite the tragic outcome of the Fated Clash. As the present, corrupted Hikari, she uses Liael=Odium from Dark States, which accumulates power into a Destined Time Piece to grant an extra turn, representing her accumulated years of repressed guilt culminating in a desire to go back and undo her past.