Edit: Added some more in-depth information about her
Empress Amaterasu is one of the leading rulers within the five eastern kingdoms east of Equestria, and to her people, she is revered similar to how Equestria sees Princess Celestia and Princess Luna. It is known that she uses her kirin magic to help raise the sun on her portion of the world, bringing forth the day when Celestia is lowering it, and vice-versa. However, while her relations with Equestria are peaceful, she continuously bickers over with her neighbors, Chineigh, and their obnoxious rulers.
She has two brothers, Susano and Tsukuyomi, the latter being her opposite by raising and lowering the moon while Susano is in charge of the weather of Neighpon. Amaterasu has only one living heir by the name of Princess Asahiko.
Please note that Empress Amaterasu is more based on the actual shinto goddess, Amaterasu-oomikami, and not Capcom's Amaterasu. Her relations will reflect the stories of Shintoism. It is a pet peeve of mine for people to bring this up, and I will not hesitate to hide your comment. Thank you <3
Empress Amaterasu © Tambelon
MLP: FiM © Hasbro