Excalibur, known as Ex, functions as the sentient holy sword belonging to the princess of the Human Kingdom's imperial army. Captured with the princess during her imprisonment by the demonic Hellhorde, Ex acts as her constant companion and advisor throughout their confinement. His origins lie within a trio of legendary swords, alongside Deus and Machina, though he remains the only one directly involved in the narrative. Physically, Ex exists solely as a sentient weapon, lacking a biological form and communicating through magical means instead of speech. This communication manifests visually as distinct square-shaped word bubbles with double borders in the manga adaptation. He requires neither sustenance nor sleep, though prolonged wakefulness can induce magical exhaustion and weakness. Though genderless, Ex is consistently referred to with male pronouns and exhibits a personality marked by rationality and exasperation, often serving as the sole voice of reason against the Hellhorde's unconventional interrogation methods. Ex's primary duty involves attempting to prevent the princess from divulging imperial secrets during the Hellhorde's "torture" sessions, which typically tempt her with gourmet food, leisure activities, or modern conveniences. He frequently interjects with concerned queries—his signature phrase being "Your Highness?"—when sensing her resolve weaken. However, his efforts are routinely thwarted by the princess's susceptibility, leading to comedic failures. His effectiveness as a weapon is compromised during captivity; at the time of capture, his original ultra-sharp blade was undergoing repairs, leaving him with a weaker temporary replacement that contributed to their defeat. Over time, Ex displays subtle development beyond his initial rigid demeanor. While starting as an aloof observer, he gradually participates in group activities orchestrated by the torturers, such as gaming sessions or leisure outings, signaling reluctant integration into the Hellhorde's social dynamics. On rare occasions when targeted directly by "tortures," he proves just as susceptible as the princess, abandoning his principled stance to avoid discomfort. His backstory reveals prior reverence for the princess as a formidable warrior, though this admiration diminishes due to her repeated capitulations during captivity. Ex's background as a living weapon forged for combat sharply contrasts with his current advisory role, yet his unwavering loyalty to the princess persists. His extensive knowledge of imperial strategies and secrets remains guarded, aligning with his duty to protect the Human Kingdom's interests even in captivity.