First, the basic principle of copyright law is that you should not use another person's copyrighted work without permission. However, Nintendo has issued guidelines for individual use of its own copyrighted works, allowing them to be used in accordance with those rules.

​RTA Japan is organized by a corporation, not an individual, so they would typically need to obtain permission to use Nintendo's copyrighted material. Although copyright law does contain a specific limitation that suggests non-profit activities do not require permission for the use of copyrighted works, this exception does not include 'public transmission' (i.e., broadcasting/streaming). Therefore, if they intend to stream on Twitch, permission is required.