Sumeōmikami is another name for the sun goddess, Amaterasu, which is also Yukiko's 2nd Persona. It is one of the names used for Amaterasu at her place of worship in Ise.
Design
In line with Sumeōmikami being another name for Amaterasu, Sumeōmikami's design is similar to Yukiko's Amaterasu, but with gold ornaments instead of silver.
In Golden, Yukiko starts with Konohana Sakuya. It transfigures into Amaterasu upon maxing her Social Link, and can further transfigure into Sumeo-Okami during winter.