He is about 35 pounds/16kg, so not a small dog, but definitely not a “large” dog.

As Harry mentioned, Japan has a much narrower definition of service dogs and your situation is likely outside of it.

The best thing would be to contact the Japan Guide Dog Association: https://www.moudouken.net/en/

They can at least point you in the right direction.

Please let us know how it goes.

We flew Delta.

How big is your dog? If it is not a trained Service Dog eligible for the same title in Japan [you can easily get this document if it is], it will very, very likely require crating in a stroller or hand luggage.