Seisan

The karate kata Seisan (十三) (alternate names Sesan, Seishan, Jusan, Hangetsu) literally means '13'.

While it is believed Seisan derives from Yong Chun White Crane Boxing from Fujian Province in Southern China, where the form is known as 'Four Gate Hands', this remains completely unproven and uncorroborated.

The version of Seisan taught in the Seibukan Shorin-Ryū syllabus can be traced back to Sōkon 'Bushi' Matsumura (a highly influential teacher to Shorin styles, hence the name Matsumura-no-Seisan).

The form predominantly features the stance Shiko-Dachi (common in Tomari-te kata) accompanying a block which often sets up a powerful pivot and punch into Zenkutsu-dachi.

Very closely resembling the Seibukan Shorin-Ryū Seisan from the same lineage the Okinawa Seidokan system traditionally teaches Matsumura-no-Seisan as the first kata in their curriculum.

Though not considered a basic kata, the Okinawa Seidokan version is foundational in teaching koshi (trunkial twist power) from a beginners onset.

Hangetsu contains many slow movements under tension, popular in Naha-te schools such as Goju-Ryū, but rare in Shotokan and Shuri-te influenced styles making the kata quite unique.

Funakoshi was taught by Sokon Matsumura (Shuri-te), Kodatsu Iha (a student of Kosaku Matsumora of Tomari-te) and Seisho Aragaki (associated with Goju-Ryū) all of which had knowledge of a version of Seisan.

Hangetsu translates to 'Half Moon' or 'Half Month' a reference to the half-moon stance used extensively and the semi-circular stepping actions in this kata.

A more obscure and unlikely theory is that the kata was taken from a Chinese folk dance where the performer is explaining the importance of the tides as they cycle on 13-day intervals as the Moon revolves around the Earth.