"Tantei Opera Milky Holmes Alternative ONE -Kobayashi Opera to 5-mai no Kaiga-" is a spin-off of the "Tantei Opera Milky Holmes" series, focusing on a self-contained narrative that diverges from the main storyline. The series centers on Kobayashi, a young detective-in-training, who is tasked with solving a mystery involving five mysterious paintings. These paintings, each depicting a different scene, are rumored to hold a hidden secret that could change the course of history. Kobayashi's investigation leads her to uncover a web of intrigue involving art collectors, rival detectives, and a shadowy organization with its own agenda.

The plot unfolds as Kobayashi encounters various characters, each connected to the paintings in some way. Among them is Opera, a mysterious and enigmatic figure who serves as both a mentor and a rival to Kobayashi. Opera's knowledge of the paintings and their secrets becomes crucial to the investigation, but her true motives remain unclear. As Kobayashi delves deeper, she discovers that the paintings are not merely works of art but are tied to a larger conspiracy involving the theft of rare artifacts and the manipulation of historical records.

The series explores themes of trust, ambition, and the pursuit of truth, as Kobayashi navigates a world where appearances can be deceiving. Her journey is marked by a series of challenges, including deciphering cryptic clues, outsmarting rival detectives, and confronting her own limitations as a detective. The narrative builds towards a climactic confrontation where the true nature of the paintings and the conspiracy behind them are revealed, forcing Kobayashi to make difficult choices that will define her path as a detective.

The main characters include Kobayashi, a determined and resourceful detective-in-training; Opera, a skilled and enigmatic figure with a deep connection to the paintings; and a supporting cast of detectives, art collectors, and antagonists who each play a role in the unfolding mystery. The series maintains a balance between lighthearted moments and tense, suspenseful sequences, creating a dynamic narrative that keeps viewers engaged. Through its focus on mystery and character development, "Tantei Opera Milky Holmes Alternative ONE -Kobayashi Opera to 5-mai no Kaiga-" offers a fresh take on the detective genre within the Milky Holmes universe.