Sumiyuki was a son of Kujô Masamoto and was adopted by Hosokawa Masamoto. Masamoto intended at first to make Sumiyuki his heir but when this caused dissatisfaction within the Hosokawa clan (who objected in view of Sumiyuki's noble blood), he came to favor a younger adopted son, Sumimoto. Sumiyuki was supported in his claim for the inheritance by Kôsai Motonaga and the two plotted against Masamoto. Masamoto was surprised and murdered in his bath in 7/1507. Around a month later, however, Sumiyuki and Motonaga were attacked by allies of Sumimoto and defeated. Sumiyuki committed suicide.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005