Some say that this is the oldest kata that is still practiced in Okinawa, but what basis they use to make this statement is unknown. Seisan means "crescent moon" or "13 steps". Some say that was the name of a famous martial artist who came to Okinawa around 1700. Some say that the kata is practiced in Fukien, China among the Fukien Shaolin Monk (Luohan) Fist, Dragon and Lion Boxing Kung Fu practitioners. In Okinawa, there are two different versions. The Naha-te version is pretty much like the Chinese, according to some sources. The Shuri-te version (which was also taught by Fusei Kise) is quite different, and evolved differently, or so they say. Some say that the Naha-te version was handed down to the Okinawans by the Chinese master Liu Liu-ko, the creator of the "Shouting Crane" style of Fukien, China. Others claim that it was brought to Okinawa by Higashionna Kanryo of Naha-te, a student of Liu Liu-ko. And others even say that it was passed down in Kunida (Kume-Mura) long before Higashionna and Liu Liu-ko came along. As for the Shuri-te version, some say that Takahara Peichin passed it down. Some claim that Matsumura also practiced it, but that claim is questionable, or at least, it is believed by some that he did not include it in his personal system.
Fusei Kise probably got it from one of his teachers who studied under Kyan Chotoku. Some claim that Kyan got it from Bushi Matsumura, but that claim is also questionable.
Some claim that early on, Hohan Soken taught a version of this kata. We have not been able to substantiate it, but it is not beyond the realm of possibility. We just know that it was not taught by him later in life. Another kata we are sure about that he apparently had and decided not to teach is Sanchin. He said that Sanchin teaches the same principles as Naihanchi, so, he said, why be redundant? This may have been the same reason he did away with his verison of Seisan, if he had one, since Gojushiho teaches the same things as it does.