Momoko Yamaguchi (山口百子 Yamaguchi Momoko) was one of the side character in Ultraman Leo. She was Gen Ohtori's love interest and she also was part of the main side cast until episode 40. She was portrayed by Kaori Okano.
The protagonist of the series - Ultraman Leo he moved to Planet Earth after his home world on planet L77 was destroyed by Alien Magma. While living on Earth as Gen Ohtori, he made his living as a coach in the Seongnam Sports Centre and his girlfriend, Momoko Yamaguchi was the member of the sport center. He also befriended two orphans that Momoko had taken care of, Toru Umeda and Kaoru Umeda whose father had been killed by Alien Tsuruk. Whenever Gen as Leo found himself unable to defeat an alien or monster threat, he would trained himself harder even by pushing his own limits. While in his training, his friends (including Momoko) were shown to be supportive for him, providing Gen the training that he needed. She sometimes helps Gen Ohtori train the children at the sports club and even aids Dan Moroboshi in training him on a few occasions. She was killed off in Silver Bloome's attack on Tokyo, along with Kaoru and Takeshi when they were went shopping on a shopping complex, everyone was attacked and killed by Black Directive's first saucer beast - Silver Bloome, whom proceed to eat the whole building.