Kashio Rigen (1565-?) was one or more go players, one of which was the teacher of Monnyusai.
For many years it was believed that Honinbo Sansa had a rivalry with a person named Kashio Rigen. However, evidence referred by Fairbairn & Hall (2009, p. 198-9) suggests that in all probability the name Kashio Rigen was a confusion based upon another text, where the two names Kashio and Rigen are immediately next to each other. This would mean that Kashio and Rigen are different people and Honinbo Sansa had a rivaly with two individuals, rather than a single person.
 Fairbairn, J. & Hall, T. M. (2009). The Go companion: Go in history and culture. Richmond, VA: Slate & Shell.