Tomoe Gozen
They are significantly different in the anime, except in appearance. Saisei and Saishi are "living dolls" that have many copies that try to overwhelm Kyo and even attack Yuya. Eventually Saisei transforms her clothes into armor and a naginata (just like the manga), and absorbs Yuya. Yuya while inside the void inside Saisei is able to destroy Saisei's core, and later Saishi's core with her gun. There is no mention of Saisei being Tomoe Gozen in the anime.