Fritz Heidenreich, known in his transformed state as Teknoman Dagger, serves as a pivotal antagonist who introduces the threat of the Teknoman system early in the narrative. Before his transformation, Fritz was a human crew member aboard the spaceship Argos, where he worked as an assistant to Dr. Aiba and was a colleague of the protagonist, D-Boy, whose real name is Takaya Aiba. His capture and subsequent alteration by the alien Radam turned him into the first fully operational Teknoman deployed to invade Earth, marking him as the initial active enemy that D-Boy must confront.

Dagger possesses a cunning and vengeful personality, distinguishing himself not just through brute force but through strategic and deceptive tactics. Unlike many straightforward antagonists, he is recognized as the most adept among his kind at using treachery and guile to achieve his objectives. A defining personal trait is his pride, which, when wounded, transforms into a deep-seated need for retribution. After losing a battle to Tekkaman Blade, he deliberately leaves a scar on his own eye to ensure he never forgets the pain and humiliation of that defeat, fueling his subsequent actions.

The primary motivations for Teknoman Dagger are to serve the Radam’s invasion of Earth and to defeat his former comrade, D-Boy. His role in the story is largely defined by the significant, lasting damage he inflicts upon the hero. While he is the first villain to battle Blade, his impact extends beyond this initial encounter. He is one of the few enemies to achieve a major strategic victory against the protagonist: by setting a trap using a fake distress signal to lure D-Boy into an orbital base, Dagger employs an interference spectrum device to shatter D-Boy’s transformation crystal. This act permanently cripples D-Boy’s ability to transform independently, forcing him to rely on the support mecha, Pegas, for the remainder of the series. In this sense, Dagger is the direct catalyst for the creation of the central partnership between Blade and Pegas.

In terms of key relationships, his history with D-Boy from their time on the Argos adds a personal layer to their conflict. He also shares a connection with Pegas, as the character shares a voice actor with the support mecha in the original Japanese version. Despite his early successes, Dagger undergoes a clear developmental arc that ends in his destruction. After proving himself a capable and cunning threat—being the only Radam Teknoman to deal such severe and lasting damage to Blade—he is ultimately defeated in a final confrontation when D-Boy successfully transforms again and overpowers him.

Regarding his abilities, Teknoman Dagger is considered the weakest among the complete Teknomen in terms of raw power, a deficiency he compensates for with his strategic mind. A peculiar and notable limitation is that he is the only fully transformed Teknoman who does not possess the Voltekka, a massive and immensely powerful energy cannon that is a standard superweapon for others of his kind. His combat style instead revolves around his primary weapon, the Tek Lancer, which is a long spear. This weapon has a unique alternate configuration: it can be deployed into the shape of a bow. In this form, he uses a powerful armament called the Cosmo Bowgun, which allows him to fire powerful energy arrows from his hands. He is also capable of firing smaller energy projectiles, described as energy daggers, from his right eye or left arm. His armor possesses regenerative capabilities when he is out of combat, and he is equipped for high-speed flight in space.