Princess Yasuko or Princess Teishi (媞子内親王, Teishi (Yasuko) Naishinō; 1076–1096), later Ikuhomon’in (郁芳門院) was an Honorary Empress of Japan to her brother Emperor Horikawa. She was the first daughter of Emperor Shirakawa and Fujiwara no Kenshi (1057-1084), and the sister of Emperor Horikawa. She served as the Saiō of her father Emperor Shirakawa in 1078-1086. In 1087, her father abdicated in favor of her brother Emperor Horikawa.In 1091, she was appointed Honorary Empress to her twelve-year-old brother the Emperor. It was rare for a sister to be appointed Empress of her own brother, but she was actually his nurse and adoptive mother, their mother having been dead since he was five.