@amanjeev I'm allergic to soy; I don't have a problem with gluten... but I know that soy sauce has soy and also gluten (and is high in sodium too).
"Coconut aminos" is a gluten-free, soy-free, low-sodium substitute for soy sauce. It could solve cooking a bit, and possibly sushi with friends.
But be careful still: some sushi has soy sauce added directly to it.
He may want to consider making a card that says to avoid gluten and (also specifically) soy sauce, in English and Japanese.