"Taboo Tattoo" is a 12-episode anime series that blends action, supernatural elements, and military intrigue. The story centers on Seigi, a skilled martial artist with a strong sense of justice, who saves a homeless man from thugs. In gratitude, the man gives Seigi a mysterious tattoo, which turns out to be a powerful weapon known as a "Tattoo." These Tattoos are ancient artifacts capable of granting their bearers extraordinary abilities, but they are also highly sought after by various factions due to their destructive potential.

Seigi's life takes a dramatic turn when he is targeted by agents from the Kingdom of Selinistan, a fictional nation seeking to collect Tattoos for their own purposes. He is joined by Izzy, a young girl with her own Tattoo and a connection to the American military, which is also investigating the artifacts. Together, they uncover the dark history behind the Tattoos, which were created as part of a secret project during World War II. The project, known as "Taboo," aimed to develop superhuman soldiers but was abandoned due to its catastrophic consequences.

As the story progresses, Seigi and Izzy face off against powerful enemies, including Bluesy Fluesy, a skilled assassin working for Selinistan, and Colonel Sanders, a high-ranking American officer with his own agenda. The conflict escalates as the true nature of the Tattoos is revealed: they are not merely weapons but also conduits for interdimensional energy, capable of causing widespread devastation if misused. The series explores themes of power, morality, and the consequences of wielding extraordinary abilities, as Seigi struggles to balance his ideals with the harsh realities of the world he has been thrust into.

The narrative is driven by intense action sequences, strategic battles, and the evolving dynamics between the characters. Seigi's growth as a protagonist is marked by his increasing understanding of the complexities surrounding the Tattoos and his determination to protect those he cares about. The series concludes with an open-ended resolution, leaving room for further exploration of its world and characters.