If Naked Snake does not set off any alerts, his codename will be "Tsuchinoko". If the player beats Portable Ops Plus on any difficulty without setting off alert mode at all throughout the game, they will receive a feather for their picture, and Tsuchinoko for their codename.

The Tsuchinoko (ツチノコ) is a legendary snake-like cryptid from Japan. The name tsuchinoko is prevalent in Western Japan, including Kansai and Shikoku; the creature is known as bachi hebi in Northeastern Japan.