Steins;Gate: Heni Kuukan no Octet/ Steins;Gate: Octet of Shifting Space

A non-canon extension of the True End of the original game. Unlike the modern visual novel format of the original game, this retro game perfectly mimics the style of graphical text adventure games from the 8-bit PC era (e.g. PC-88), with the player typing short commands to interact with and explore the game world. It features all backgrounds and characters drawn in a low-color pixelated style with emulated scanlines, chiptune music played through an emulated FM chip, and no voice acting. Although non-canon, the game contains many easter eggs and references that connect Chaos;Head and Steins;Gate together.

The premise of the game features Okabe receiving a D-Mail from himself in 2025 that states that he must save the future by reclaiming an IBN 5100 from a person under of the alias "Knight-hart". This person is Takumi Nishijō of Chaos;Head, as he runs under the same player name in his favorite MMORPG, and the D-Mail stating that "Neidhardt" lives in Shibuya and has "inherent, supernatural abilities", a reference to his power as a gigalomaniac.