Nintendo's aggressive stance against emulation and piracy is well-documented. Recent legal actions highlight this, including a $2.4 million settlement with Yuzu emulator developers in March 2024, the cessation of Ryujinx development in October 2024 following Nintendo's intervention, and legal pressure on the Dolphin emulator's Steam release in 2023. The infamous 2023 case against Gary Bowser, who resold devices allowing Nintendo Switch piracy, resulted in a $14.5 million judgment.

Now, a Nintendo patent attorney, Koji Nishiura, has shed light on the company's legal strategy. Speaking at Tokyo eSports Festa 2025, Nishiura clarified that while emulators aren't inherently illegal, their use can become illegal depending on their functionality. Specifically, emulators that copy game programs or bypass console security measures may infringe on copyright laws.

This legal basis rests largely on Japan's Unfair Competition Prevention Act (UCPA), limiting Nintendo's extraterritorial reach. The R4 card for the Nintendo DS, which enabled piracy, serves as a key example. Nintendo's successful 2009 lawsuit against R4 manufacturers and sellers, based on UCPA violations, effectively banned its sales in Japan.

Nishiura further emphasized that tools facilitating pirated software downloads within emulators, termed "reach apps" in Japanese law, also violate copyright. Examples include the 3DS's "Freeshop" and the Switch's "Tinfoil."

Nintendo's lawsuit against Yuzu cited one million pirated copies of The Legend of Zelda: Tears of the Kingdom, alleging that Yuzu's Patreon generated $30,000 monthly from subscribers receiving early access and exclusive features. This underscores Nintendo's focus on combating both emulation and the distribution of pirated content.