Assassin is the Assassin-class Servant able to be summoned by the Protagonist in the Grand Orders of Fate/Grand Order.
Stheno was the first daughter of the Gorgon Sisters, the older sister of Euryale and Medusa, who were goddesses born from the wishes of mankind for ideal idols, the embodiment of the yearning hearts of men. While she and Euryale were "perfect goddesses" who would not age, Medusa had some kind of flaw that allowed her to grow. They should have been three united sisters, but this divide allowed them to become three separate individuals. While Medusa was different from the start, her existence also brought irregularities in the two who were still the same. Due to the jealously of Athena, Medusa was cursed, had the faith of her followers taken away, and was banished to the Shapeless Isle as a monster. She called Stheno and Euralye monsters because they would never grow old, but that was a lie to cover the fact that they were "perfected goddesses."
Stheno was pictured as the "ideal woman", displaying an elegant demeanor, an overflowing grace, and the wisdom in her actions and words. It is said that men will lose their senses over the rapturous feeling and swear eternal loyalty to her should just their names pass from her lips. Unlike their younger sister who is an expert in fighting and disliked humans, she and Euryale perfect themselves as idols who liked humans, welcoming the men visiting the island, comforting them, and sending them on their adventure. Though her image on the surface seems to paint that as the very meaning of her existence, that is only to those observing them from afar. She is a devil who loves everything pretty and cute, freely and unconditionally. While she loves humans, it is not as "living beings", but rather in the way of toying with those she likes, embarrassing and driving them to ruin while watching them struggle. In reality, they truly hate men, while their sister is the one who bares them no ill will. They, loved by men, should be destined to be violated by them day after day. Though she despised her fate, Stheno had given up until Medusa became the one to protect them.
Stheno and Euryale appear briefly in Carnival Phantasm Episode 12.
