Kyan learned Seisan from his father, Kyan Chōfu 喜屋武 朝扶, who was a student of Matsumura Sōkon.
Key points from Shimabukuro Hanshi:
Seisan is the tanren 鍛錬 kata for Seibukan. It forges the body for our kind of karate. When asked how to improve in Seibukan karate, Shimabukuro Hanshi responded, "Do Seisan."
Repeated use of shiko dachi builds the legs and waist to develop stability.
Kyan emphasized jumping towards and away from an attacker.
Renzoku tsuki geri is unique to Matsumura's Seisan and develops continuous attacking.
Adapted from the Seibukan book by Shimabukuro and Smith