E.I.N. is a creature in the Soul series of fighting games. His first appearance was in the series' sixth installment, Soulcalibur V. He is a werewolf-like spirit that Z.W.E.I. can summon during battle. He is referred to as a minion in Z.W.E.I.'s profile, thus confirming E.I.N. is a being inferior to him.
The name of the weapon E.I.N. is an acronym that spells out "ein", the German indefinite article "a" or "one" (the correct German term for the number "1" would be "Eins", "ein" is used in combination with a noun, e.g. "ein Haus", "a/one house"), while its wielder Z.W.E.I. spells out "Zwei", the number "2".
- Minion of Z.W.E.I.
- A wolf spirit similar to E.I.N. floats behind the final boss character Unknown in Tekken Tag Tournament. There is no confirmed relationship between the two characters.
- E.I.N. is considered by the game to be Z.W.E.I.'s primary weapon; Z.W.E.I.'s alternate weapons are all different colourations of E.I.N. rather than different swords. However, Z.W.E.I.'s sword Kreuzgriff changes color based on the chosen version of E.I.N.
- E.I.N. first appeared to save Z.W.E.I.'s life when the latter was to be executed for defying Graf Dumas.
- E.I.N.'s origins are currently unknown, even to Z.W.E.I.