Immortal Assassin is the 13th rank in the game. It costs 2.5Si coins. It gives the player a x175 Ninjitsu multiplier. It costs 1.62Si coins if you own the Masterful Wrath Element and the Blazing Entity Element. Equipping this rank will emit a red aura and red and blue flames around the player's torso, hands and legs, and red and blue lightning particles around the player's torso.
The Eternity Hunter rank can be unlocked upon purchasing this rank.