Hassan of Serenity holds the title of one of the nineteen Hassan-i-Sabbah, leaders of the Hashashin assassination order. Her alias stems from unparalleled mastery of poison. Her body serves as a lethal weapon; skin, nails, and bodily fluids carry deadly toxins fatal through minimal contact. This condition arises from her existence as a "Poison Girl" (Visha Kanya), a human weapon engineered by the Assassins for covert elimination. Her inherently toxic physical form renders any intimate contact fatal, defining her existence and methods.

Within the *Fate/Grand Order* Camelot movie, she manifests as an Assassin-class Servant allied with the protagonist in the Sixth Singularity. She participates in the resistance against the tyrannical Holy City established by the Knights of the Round Table. The film streamlines the game's narrative, emphasizing her rescue by the protagonists as a key step in consolidating support from the Hassans. Her involvement contributes directly to the efforts to besiege the Holy City and confront the Lion King's forces.

Her Noble Phantasm, **Zabaniya: Delusional Poison Body**, embodies her legend as a poison master. It manifests as a corporeal curse where touch or bodily fluids inflict rapid, fatal poisoning. This Anti-Unit technique assassinates targets through direct physical interaction, reflecting her lifetime of using her body as a tool. The poison's potency bypasses conventional defenses.

Personality-wise, she exhibits obedience and calmness, consistent with her "Serenity" epithet. Her interactions reflect quiet resignation to her poisonous nature, coupled with unwavering loyalty to those resistant to her toxins. This stems from her history of isolation and the psychological toll of her existence.

Broader *Fate* media reveals her origin in *Fate/Prototype: Fragments of Sky Silver*, where she accidentally caused her first Master's death via her poisonous body. This led to a contract with Manaka Sajyou and complex emotions toward Tatsumi Kitano. These elements remain unaddressed in the Camelot movie, which treats her as a standalone Servant summoned for the Grand Order conflict. Her Spirit Origin carries a unique limitation: experiencing genuine love causes her to cease existing entirely, preventing re-summoning with the same memories.

The Camelot film condenses her role, omitting connections to figures like Arash or Paracelsus. Her design adheres to her standard depiction: short violet hair, form-fitting black attire, and the characteristic Hassan skull mask. Her third Ascension form in related media reveals a natural beauty historically used to lure targets, though the film retains her base design without delving into ascension stages or Shapeshifting. Her character remains focused on the collective struggle against the Singularity's threats.