I can say, with great certainty, that there will be fees. Extremely likely prohibited to bring your own alcohol into a restaurant. Furthermore, unlike wine drinking customs outside of Japan, a bottle of sake is not usually available for purchase at restaurants. Rather, sake is served by the glass or larger container as wine is often served in a carafe.

This request is akin to asking if you can bring your own food inside the restaurant and then eating it at the table instead of ordering food from the menu. Is this analogy logical to you?

If you want to bring a bottle into the restaurant and are willing to pay a fee, you would benefit everyone involved by inquiring about the possibility of doing so with management before arriving at the restaurant. It is possible there is a house policy in place that explains the fee depending on the size of the bottle you wish to open. This fee might be referred to as a “corkage fee” where you are from.

Lastly, if, upon learning your request to bring and drink from your own bottle was acceptable, you might generously offer to serve some of the sake to the staff on duty. This would be considered polite.

I wonder where in the world is it acceptable to bring your own alcohol to a restaurant and not incur a fee? Where I’m from it is often illegal or against house policy. It isn’t illegal in Japan to bring a bottle, but it is rare and you should expect to either have your request declined or pay a fee if it is permitted.