No door can Not be opened with a Non-black key is a puzzle action video game developed by Studio ZeF and published by Marvelous.

About

No, Non, Not!

No door can Not be opened with a Non-black key is a rule-modifying 2D action puzzle game in which the protagonist, who has the power to manipulate the word “Nai” (no / non / not), adventures through a world created by rule sentences.

Summoned by a goddess, the protagonist is given the ability to manipulate negation and must solve a number of stages in order to rescue the princess.

The protagonist can use the given ability to retrieve the negative word “Nai” from a rule statement and then add it to other rule statements.