The elite units of the Saints and Heroes unit pack for Shogun 2 are titled off of actual prominent figures of Japanese history.
Seigen's Swordmasters comes from Toda Seigen, a famous swordsman. Funnily, he was famed for his short sword technique - putting his name to the unit may be been inspired by how it's been said Seigen taught Sasaki Kojiro, the famous rival of Miyamoto Musashi whose favorite weapon was a nodachi.
Yoritomo's Yabusame Cavalry is probably named after Minamoto no Yoritomo, the ultimate victor of the Genpei War and the founder of the Kamakura shogunate, who particularly had his warriors be trained in the mounted archery practice of Yabusame.
Tokitaka’s Tanegashima is named after Tanegashima Tokitaka, the lord of the Tanegashima island who purchased two matchlock muskets from the Portuguese and had a blacksmith to try and copy the mechanism, though it wasn't until a Portuguese blacksmith came to Japan a year later that they could actually be reproduced. The weapons were, of course, named after the island.
Kiyomasa's Katana Cavalry is named after Kato Kiyomasa, a real Blood Knight that was one of the Seven Spears of Shizugakate.