"Onegai Lifesaver" is a manga series that centers around the life of a high school student named Kaito, who becomes entangled in a series of supernatural events after encountering a mysterious girl named Yuna. Yuna, who possesses the ability to manipulate time, reveals that she is a "Lifesaver," a being tasked with preventing tragic deaths and altering the course of fate. Kaito, initially skeptical, is drawn into her mission when he discovers that his own life is connected to a series of impending disasters.

The narrative unfolds as Kaito and Yuna work together to identify and save individuals marked for untimely deaths. Each arc focuses on a specific person or group facing a life-threatening situation, often tied to unresolved personal struggles or societal issues. Yuna's time-manipulation abilities allow her to rewind events and create opportunities to change outcomes, but her powers come with limitations and consequences, adding tension to their efforts. Kaito, while initially a reluctant participant, gradually becomes more invested in their mission, driven by a growing sense of responsibility and empathy for those they aim to save.

As the story progresses, the relationship between Kaito and Yuna deepens, revealing layers of complexity in their partnership. Yuna's past and the origins of her abilities are gradually uncovered, shedding light on the broader implications of her role as a Lifesaver. The series explores themes of fate, free will, and the moral dilemmas of altering destinies, as Kaito and Yuna grapple with the ethical implications of their actions. Supporting characters, including classmates and individuals they encounter during their missions, contribute to the emotional weight of the narrative, often serving as catalysts for personal growth and reflection.

The plot is structured around episodic arcs, each resolving a specific crisis while advancing the overarching storyline. The stakes escalate as Kaito and Yuna face increasingly dangerous and morally ambiguous situations, culminating in a confrontation with forces that challenge the very nature of their mission. The series balances moments of action and suspense with introspective scenes, creating a dynamic and engaging narrative. Through its exploration of human connections and the consequences of intervention, "Onegai Lifesaver" presents a thought-provoking examination of life, death, and the power of choice.