VGFacts

Throughout the game, there are several NPC Revenants that are references to Team Ninja's works:

Shibasawa Kou - The game's producer
Samurai Gaiden - Ninja Gaiden
Shadow Warrior - The European name of Ninja Gaiden
dropped_by_izuna - The Izuna Drop move from Ninja Gaiden and Dead or Alive
theJaquio - The main villain from Ninja Gaiden
Holy_San - Holy Vigoor Emperor from Ninja Gaiden Black
Genshin07 - Genshin from Ninja Gaiden II
KarmicPunishment - the curse from Ninja Gaiden 3
IreneIsMyHero - Irene Lew from Ninja Gaiden
Dr. Smith - Walter Smith from Ninja Gaiden
oinin_AYANE - Ayane from Dead or Alive
nukenin_KASUMI - Kasumi from Dead or Alive
ZACK - Zack from Dead or Alive
Hajinmon4Life - Ayane's fighting style, Hajin Mon
RebootRygar - Rygar
GITAROO-MAN - Gitaroo Man
GARI - Dr. Gari from Tecmo Secret of the Stars