"A Wish of My Sister" is a manga series that explores themes of family, sacrifice, and the supernatural. The narrative centers on two siblings, Haruto and Yuna, whose lives are upended when Yuna is diagnosed with a terminal illness. Desperate to save his sister, Haruto encounters a mysterious entity that offers him a chance to alter Yuna's fate. However, the deal comes with a heavy price: Haruto must sacrifice his own lifespan to extend Yuna's. Reluctantly, he agrees, setting off a chain of events that intertwines their destinies with supernatural forces.

As the story progresses, Haruto and Yuna discover that the entity's intervention has unintended consequences. Yuna's prolonged life begins to attract malevolent spirits, forcing the siblings to confront a series of supernatural threats. Haruto, now burdened with the knowledge of his shortened life, struggles to protect Yuna while grappling with his own mortality. The siblings' bond is tested as they navigate a world where the boundaries between life and death blur.

The manga delves into the emotional complexities of their relationship, highlighting Haruto's selflessness and Yuna's guilt over her brother's sacrifice. Supporting characters, including a enigmatic exorcist and a childhood friend, play pivotal roles in aiding the siblings as they face increasingly dangerous supernatural phenomena. The narrative builds tension through a mix of emotional drama and supernatural suspense, culminating in a climactic confrontation with the entity that orchestrated their plight.

Themes of love, loss, and the lengths one will go to for family are central to the story. The manga balances its supernatural elements with heartfelt moments, creating a poignant exploration of sibling devotion in the face of insurmountable odds. The resolution of the series ties together the emotional and supernatural threads, leaving a lasting impact on the characters and their journey.