@MisterMango I mean there are plenty of dishes that combine both chicken and seafood. Paella and Jambalaya off the top of my head. Also, it's common in Asian cuisines to use seafood based sauces such as oyster and fish sauce to season meat. It's not like they need to keep kosher, they're Japanese. Chicken cooked in dashi broth with bonito flakes is also fairly common in Japan.
Edit: Found this pic lol. It's a Japanese store-bought bento box with fried fish and chicken together.
Edit2: Thought I'd mention that you don't really want to
cook fish and chicken together or even in the same uncleaned pan one after the other, because you don't want to mix up the flavor profiles. In addition, fish and chicken take different amounts of time to cook, so mixing can lead to under or overcooked food and possible contamination with pathogens. Also this is usually not an issue, but fish oils go rancid fast, so mixing that in with the chicken will reduce the latter's lifespan in the fridge.