Hassan of the Cursed Arm ranks among the nineteen holders of the Hassan-i-Sabbah title, leading the Middle Eastern assassination order that birthed the term "assassin." To claim this mantle, each Hassan forges a unique lethal art called Zabaniya. His technique, Delusional Heartbeat, originated from grafting the demon Shayṭān’s right arm onto his body—replacing his original limb through a ritual that sacrificed his face and identity, leaving only a blank visage beneath his skull mask. The grafted arm typically appears as a bandaged, flattened stump but unfolds into a functional limb. Its core ability conjures an ether replica of a target’s heart; crushing this phantom destroys the actual heart across any distance or barrier. This power exclusively affects humans, failing against demon-cursed entities or those lacking standard biology. As a final measure, forcibly detaching the arm unleashes the uncontrolled Shayṭān to indiscriminately consume souls—likely including Hassan’s own.

In *Fate/Grand Order The Movie Divine Realm of the Round Table: Camelot*, he emerges during the Sixth Singularity under the Lion King’s rule over Jerusalem. Hassan allies with Chaldea’s protagonists after they uncover a hidden map to his mountain village sanctuary—revealed when sunlight interacts with a red gem pendant worn by a local boy, Rushd. Hassan bears an identical gem, suggesting a link to Rushd’s lineage. He safeguards the village and its inhabitants, organizing resistance against the Lion King’s forces. During a pivotal clash with the Knight Tristan—who slaughtered villagers and mutilated fellow Hassan Serenity—Hassan activates Zabaniya: Delusional Heartbeat, crushing Tristan’s heart to lethal effect. The battle culminates in Hassan’s demonic arm being severed amid the collapsing city’s destruction; he plummets from a great height without reappearing, implying his demise in this adaptation—a departure from narratives where he survives.

Consistently, Hassan displays unwavering loyalty to his Master or cause upon contracting, rooted in his devotion to the Hashashin sect’s doctrines. His personality merges ominous professionalism with profound dedication to the Saracen people and individuals like Rushd. This contrasts his self-view as an unexceptional Hassan compared to peers like Hundred Faces or Serenity. His dynamic with First Hassan, the order’s founder, involves stern judgment: First Hassan condemns the grafted arm as folly requiring atonement through death, a critique Hassan accepts without bitterness. Within the Camelot singularity, his arc highlights sacrifice—protecting the vulnerable village and deploying his cursed power decisively against Tristan, costing his arm and potentially his life. His methods and demeanor embody the assassin’s creed: operating from shadows, perfecting a single lethal craft, and erasing selfhood for duty.