In many izakaya a small dish arrives as soon as you sit down. It's automatic, it's charged as a cover (often a few hundred yen each), and it's rarely vegan. It can be fish, egg, meat, or vegetables simmered in dashi. Staff may not think to mention it. Ask when you sit down, before it arrives: some places can make it vegan. Skipping it isn't always possible: it doubles as a seat charge, and some places see refusing it as rude. It's a normal custom, not a scam. If it can't be changed, you may still pay the small cover: that's normal too.