Steins;Gate: Heni Kuukan no Octet

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.