That name is Yakumo - S1.E21

Riku wakes up and finds himself in another part of Fukumaden. He is then attacked by a masked Toujinshi named Taishin and his Shikigami, Shousetsu no Magahoshi. They think that Riku is the Ten-ryuu Toujinshi named Yakumo. With Kogenta unconscious, all Riku can do is run away, using Toujinfu to help him escape. Outside the Fukumaden, Masaomi appears and learns of the news that Riku is gone. Masaomi, Nazuna, and Souma return to the rocky mountain sector of Fukumaden to search for Riku. They are soon confronted by Mizuki and Kanna. When Riku is cornered, the real Yakumo appears and summons Buryune to fight the masked Toujinshi and Magahoshi, who are actually a part of a faction called the Jin-ryuu.