The True Name of the Heroic Spirit of the Class Card is Hassan-i-Sabbah, summoning one of nineteen wraiths depending on the user. The Hassan-i-Sabbah utilized by Shinji is unnamed. The Hassan is said to have been "an assassin that implanted an evil spirit into their right arm." The description matches that of Hassan of the Cursed Arm, but the abilities and Zabaniya of the Hassan utilized by Shinji differ slightly, with "signs of medical and industrial procedures performed after the spiritual transplant are visible".
Including the Assassin Class Card grants one of the many roped daggers that make up Assassin's arm as a weapon, similar to a whip or a rope dart.
Installing the Assassin Class Card grants the power of Assassin, including an arm made up of the intertwining roped daggers, which can continue to function even when severed and blades mounted in the user's feet. It also allows the user to utilize the Assassin's Noble Phantasm, Zabaniya: Dead Heartbeat Melody.