Hyoma Muroga is a member of the Kouga Manjidani clan and a central figure in the narrative of Shinobi: Heart Under Blade. He holds the position of second-in-command to the clan's elder, Danjo, and is the maternal uncle and former teacher of the young protagonist, Gennosuke Kouga. A seasoned and disciplined ninja, Muroga is defined by his profound loyalty to his clan and his unwavering support for Gennosuke's vision of ending the ancient blood feud with the rival Iga clan.

Physically, Muroga is recognized by his long black hair, his black attire, and three small circular markings that are vertically aligned on his forehead. The most striking feature of his appearance, however, is that he almost always keeps his eyes shut. This is not a disability but a deliberate act of extreme self-control, born from the nature of his most formidable ability.

Muroga possesses a powerful dōjutsu, a secret eye technique passed down through his family's bloodline. This ability allows him to manipulate the will of anyone who meets his gaze, compelling them to turn their own killing intent against themselves, often forcing them to commit suicide. Unlike his nephew Gennosuke, who can activate his dōjutsu at will, Muroga's version of the technique is permanently active. This forces him to keep his eyes perpetually closed to avoid accidentally harming allies or innocent people. To compensate for his lack of sight, Muroga has honed his other senses to a superhuman degree. His hearing, in particular, acts as a form of radar, allowing him to detect the precise number of approaching enemies, distinguish their gender, and perceive their movements from vast distances, making it impossible for anyone to surprise him. In combat, he is a highly proficient swordsman who favors a style that uses his sword and its scabbard in unison.

In terms of personality, Muroga is cautious, intuitive, and wise. He is the first among the Kouga to suspect that the Hattori truce, a pact of non-aggression with the Iga, has been broken. Despite his inherent distrust of the Iga, he deeply respects Gennosuke's ideals and supports his quest for a peaceful resolution between the two clans, placing his faith in his former student's leadership even when it places him in great personal danger. In many ways, Muroga is the architect of Gennosuke's worldview. His most important lesson to his young nephew was that despite the cultural and historical differences between people, they are all fundamentally human beings who live, feel, and die in the same way. This teaching is the very foundation of Gennosuke's desire for harmony over revenge.

Within the story, Muroga serves not only as a powerful warrior but also as a strategic advisor and a protector. He is often seen guiding the group's actions based on his keen senses and logical deductions. His relationship with Gennosuke is the most significant of his life; he is a mentor who has nurtured the young leader's skills and philosophy, and he is willing to sacrifice his own life to ensure Gennosuke's survival and the success of his mission. During a critical confrontation with the Iga warrior Koshirou Chikuma, Muroga orders his comrades to flee, staying behind to hold off the enemy alone. Aware that his dōjutsu is ineffective against the already-blind Koshirou, he fights a desperate battle. Muroga is ultimately struck down, but his death is a testament to his character. He does not fall; he remains standing, propped up by his own sword, having died on his feet in a final act of defiant honor and devotion to his nephew.