"Immortal Rain," also known as "Meteor Methuselah," is a manga series written and illustrated by Kaori Ozaki. The narrative centers around Rain Jewlitt, a man cursed with immortality, and Machika, a young girl seeking revenge for her grandfather's death. The story unfolds in a world where advanced technology coexists with remnants of ancient civilizations, creating a unique blend of science fiction and fantasy elements.

Rain Jewlitt, known as the "Immortal Methuselah," has lived for over 600 years due to a mysterious curse that prevents him from dying. His immortality has made him a target for bounty hunters and those seeking the secret to eternal life. Despite his long existence, Rain remains a kind and gentle soul, often helping others while trying to avoid drawing attention to himself. His life takes a dramatic turn when he encounters Machika, a spirited and determined girl who initially seeks to kill him, believing he is responsible for her grandfather's death.

Machika's grandfather, Zol the Grim Reaper, was a renowned assassin who had a complicated relationship with Rain. After Zol's death, Machika inherits his mission to kill Rain, but as she spends more time with him, she begins to question her assumptions about his guilt. The two form an unlikely partnership, embarking on a journey that explores themes of mortality, redemption, and the search for meaning in an ever-changing world.

Throughout the series, Rain and Machika encounter a diverse cast of characters, each with their own motivations and connections to Rain's past. These include Eury, a former assassin with a tragic history tied to Rain, and Yuca, a scientist obsessed with unlocking the secrets of immortality. The narrative delves into Rain's backstory, revealing the origins of his curse and the impact it has had on those around him. As the story progresses, the characters confront their own fears and desires, leading to moments of intense emotional depth and character development.

The plot is driven by a series of interconnected arcs that balance action, mystery, and introspection. The manga explores the consequences of immortality, not only for Rain but also for those who seek it. The interplay between Rain's eternal life and Machika's finite existence creates a poignant contrast, highlighting the fleeting nature of human experiences. The series also examines the ethical implications of scientific advancements, particularly in the pursuit of eternal life, and the moral dilemmas faced by those who wield such power.

"Immortal Rain" is characterized by its rich world-building and intricate storytelling. The manga seamlessly weaves together elements of science fiction, fantasy, and drama, creating a narrative that is both engaging and thought-provoking. The relationship between Rain and Machika evolves from one of hostility to mutual respect and affection, serving as the emotional core of the series. Their journey is marked by moments of humor, tragedy, and hope, making "Immortal Rain" a compelling exploration of life, death, and the enduring human spirit.