The History of Hangetsu
Tomari Seisan as it can be found today traces back to Ryukyu Kempo, a style named by Oyata Seiyu. Interestingly, Oyata received his Seisan from Nakamura Shigeru, the same man who taught Odo Seikichi of Okinawa Kenpo. Not so coincidently, the “Tomari Seisan” of Ryukyu Kempo and “Seisan” of Okinawa Kenpo are identical. The snag is that Nakamura Shigeru’s Seisan came from Kuniyoshi Shinkichi. Kuniyoshi was one of the primary students of Sakiyama Kitoku, the travel mate of Nakaima Kenri (Ryuei Ryu) and one of the individuals who brought Seisan concepts back to Okinawa. Sakiyama is largely grouped into the Naha vein of things, and Kuniyoshi lived in Nago village. As such, Okinawa Kenpo’s Seisan has virtually nothing to do with Tomari, and thus Ryukyu Kempo’s Seisan also has little to do with Tomari. It might be argued that both Nakamura Shigeru and Oyata Seiyu had Tomari influence in their arts, which is true (Nakamura with Motobu Choki and Oyata with earlier experiences before Okinawa Kenpo). But as we have seen many instructors were influenced by Tomari, some much more than Nakamura and Oyata (namely Kyan), and thus we would be teeming with Tomari Seisans if everyone affected by Tomari was labelled as such. Furthermore, the Okinawa Kenpo Seisan is well documented to have come from Kuniyoshi and is preserved in form by both Okinawa Kenpo and Ryukyu Kempo. Possible differences in bunkai alone would not warrant such a geographical name change.
As of this writing I have not uncovered the explanation for this matter.
View below Oyata Seiyu Sensei demonstrating Tomari Seisan (located at 2:43 in video) and Odo Seikichi Sensei performing Seisan: