Why an M-Rated Game Never Existed on the Original Game Boy

Effectively, no. The original Game Boy and Game Boy Color had tiny screens, 4-color palettes, and minimal audio—unsuitable for mature content. Nintendo's brand targeted families and kids; an M-rated title would contradict that identity. The ESRB launched in 1994, years after the Game Boy (1989), and Nintendo avoided M ratings to keep the platform accessible. An M-rated cartridge would alienate the core handheld audience and retailers. Some Game Boy games had dark themes (Metroid II, Castlevania), but none approached M-rated content.