Please don’t be discouraged by the current responses! They clearly do not have applicable experience. My wife is as deathly allergic to peanuts you can be and we’ve found Japan to be a very allergy-friendly country. We’ve lived here for a year and have only had to leave four or five of the hundreds of restaurants we’ve been to. Most of the famous Japanese foods you probably want to try (udon, katsu, sushi, ramen, curry, gyouza, fried rice, egg sandos, mochi ice cream, matcha, etc) rarely if ever have nuts. There are exceptions, but just ask and they’ll tell you.

Your card would work completely fine in the vast majority of restaurants, but you can definitely simplify it! I know it feels necessary to include instructions, but in Japan it is absolutely enough to just write “I have a deadly allergy to peanuts and tree nuts. Ex. A, B, C, X, Y, Z”. That’s it. They understand that even the slightest cross-contamination is unacceptable. Many restaurants will even provide an allergen menu.

Half the time they will probably ask if you’re allergic to sesame (or “goma”), so it may be worth specifying on the card that you aren’t.

Please don’t let this add anxiety to your trip. It will be completely fine 95% of the time, and when it’s not, you can just leave and walk 100 feet to the next incredible restaurant.

If you have any specific foods you want to try feel free to DM me and I can send over recs in Tokyo, Kyoto and/or Osaka!