There is a local Japanese app called tabelog, which supports online reservation, and the reviews in it are very fair, so you basically won't step on the mine by choosing a restaurant with a high rating. But it's all in Japanese, so it's a bit tricky to use on Android.

I recently found a small program "Japan's most in reservation", this can be booked in Tokyo restaurants, the whole Chinese interface, support for online payment, and Chinese customer service, is that the store is relatively small, but the small program itself is quite reliable, it is worth recommending.