Most game hardware is inevitably modded. That means if there are secret messages in the code, people will probably find them.
While user Bakueikozo was modding the Famicom Mini, the following was apparently found in the console's coding:
This is the hanafuda captain speaking. Launching emulation in 3...2...1. Many efforts, tears and countless hours have been put into this jewel. So, please keep this place tidied up and don't break everything! Cheers, the hanafuda captain.
You can see the full code in the tweet below:
— ひろみつ(85.1kg) (@bakueikozo) January 6, 2017
Neat, huh? Nice hanafuda reference, too.
As Kotaku previously reported, the Famicom Mini's Western cousin is already being modded, too, so the same message might be in the NES Mini.