"Ginga Tetsudō 999 ~Niji no Michishirube~" is a two-episode OVA that serves as a continuation of the original "Ginga Tetsudō 999" series, expanding on its themes and narrative. The story is set in a distant future where humanity has colonized the stars, and the titular Galaxy Express 999, a space train, travels across the galaxy, offering passengers the chance to obtain mechanical bodies for immortality. The protagonist, Tetsuro Hoshino, is a young boy who embarks on a journey aboard the 999 to seek revenge against Count Mecha, the man who killed his mother. Along the way, he is accompanied by Maetel, a mysterious and enigmatic woman who bears a striking resemblance to his mother.

In this OVA, Tetsuro and Maetel continue their journey through the cosmos, encountering new worlds and civilizations. The narrative explores themes of identity, humanity, and the consequences of technological advancement. Tetsuro grapples with his desire for revenge and his growing understanding of the complexities of life and death. Maetel, whose true motives and origins remain shrouded in mystery, serves as both a guide and a foil to Tetsuro, challenging his perceptions and pushing him to confront deeper truths about himself and the universe.

The OVA introduces new characters and revisits familiar ones, weaving a tapestry of interconnected stories that highlight the diversity of life in the galaxy. Each episode presents a self-contained narrative while contributing to the overarching journey of Tetsuro and Maetel. The series maintains the philosophical undertones of the original, questioning the value of immortality and the essence of what it means to be human. The Galaxy Express 999 itself remains a central symbol, representing both the promise of new beginnings and the inevitability of change.

Through its episodic structure, "Ginga Tetsudō 999 ~Niji no Michishirube~" delves into the lives of those who cross paths with Tetsuro and Maetel, offering glimpses into their struggles, dreams, and regrets. The OVA retains the melancholic yet hopeful tone of its predecessor, blending moments of introspection with action and adventure. Tetsuro's journey is not just a physical one but also an emotional and philosophical exploration, as he comes to terms with his past and contemplates his future. The series ultimately reinforces the idea that the true value of life lies not in its length but in the experiences and connections forged along the way.