Nintendo's aggressive stance against emulation is well-documented. The company's legal actions against emulator developers, like the $2.4 million settlement with Yuzu developers in March 2024 and the cessation of Ryujinx development in October 2024 following Nintendo's intervention, highlight this. Even the popular GameCube and Wii emulator Dolphin faced pressure from Nintendo, leading Valve to advise against a full Steam release. The high-profile case against Gary Bowser, resulting in a $14.5 million debt for reselling devices that bypassed Nintendo Switch anti-piracy measures, further underscores Nintendo's commitment to protecting its intellectual property.

Recently, a Nintendo patent lawyer, Koji Nishiura, shed light on the company's approach. At Tokyo eSports Festa 2025, Nishiura explained that while emulators aren't inherently illegal, their use can become illegal depending on how they function. Specifically, emulators that copy game programs or disable console security measures may infringe on copyright. This is largely based on Japan's Unfair Competition Prevention Act (UCPA), although its extraterritorial reach is limited.

The Nintendo DS "R4" card served as a case study. This device allowed users to bypass security and run pirated games. Following a lawsuit involving Nintendo and 50 other software companies, the R4 was effectively outlawed in Japan in 2009 due to UCPA violations.

Nishiura also pointed out that third-party tools facilitating pirated software downloads within emulators, such as the 3DS "Freeshop" and Switch's "Tinfoil," also constitute copyright infringement under Japanese law. Nintendo's lawsuit against Yuzu cited one million pirated copies of The Legend of Zelda: Tears of the Kingdom, linking the emulator's Patreon revenue to this alleged infringement.