In a note on its Developer Portal, Apple says (https://developer.apple.com/news/?id=09232019a) starting in October, the Japan Consumption Tax (JCT) will increase from 8% to 10%, resulting in a price increase for apps on the App Store and in-app purchases (excluding auto-renewable subscriptions) in Japan.
Once the change goes into effect, the Pricing and Availability section of My Apps will be updated and your proceeds will be increased accordingly. Developers can change the price of their apps and in-app purchases (including auto-renewable subscriptions) at any time in App Store Connect. For subscriptions, they have the option to preserve prices for existing subscribers.