Himeko Se (瀬 一三子 Se Himiko) is a beautiful spiritualist, and a major character in the Miyu OVA. She is an expert in Buddhist magic and protection rituals.
Her first encounter with Miyu and Larva, in the episode "Unearthly Kyoto", was in Japan's old capitol of Kyoto during a heat wave, where she was hired to investigate why a young girl named Aiko became comatose, and try to cure her. At the same time, a number of vampiric killings was causing concern within the city. Although Himeko suspected Miyu as the culprit, she found that the girl was in fact possessed by the shinma Raen which Miyu dispensed with... tragically, at the cost of Aiko's life. Miyu could've saved the girl by turning her into a vampire - but Himeko prevented it.
The next time, in the episode "A Banquet of Marionettes", a number of disappearances had plagued a school where a shinma, Ranka, was about. Seemed that a young boy, Kei, was wishing for immortality and had approached Ranka about it. But Miyu was also stalking the boy, and was shocked to find that Kei had fallen in love with Ranka, with Ranka doing the same. Knowing it was useless to part them, Miyu banished both of them to the darkness.
The third time, in the episode "Fragile Armor", Miyu had approached Himeko with a problem. Larva had been imprisoned by a strange spell cast by the shinma Lemures. At the same time, a suit of Japanese armor, animated by the soul of a human bonded to it by Lemures - and bound using another soul - stalked them. Himeko was able to use her magic to keep the suit at bay, but the second time around was prevented doing this by Lemures. Rather than banishing the shinma, Miyu destroyed Lemures - with the help of a freed Larva. The suit of armor, however, refused to believe it was human at first, and Miyu left it to the devices of the police, who were called to stop it. But then the suit saw the truth, but was shot to death before it could plead for mercy.
But it was the final time that Himeko met Miyu, in the episode "Frozen Time", that she found the true - and horrifying link - between them. Recalling old memories from her home town, she traveled an old road, where she found a large house - which held the perserved forms of Miyu's mother and her father. Miyu was there as well, where she proceeded to tell Himeko the story of how, 50 years before, her thirst for blood made itself evident, on how she ran upon discovering her destiny to become Earth's guardian - which caused a large number of shinma to escape the darkness, and on how she was made immune to all the vulnerabilities of vampires to get them back.
Then Himeko woke up. At first believing the whole thing was just a dream, Himeko remembered something Miyu had told her. Then Himeko put all the horrifying connections together!
When she was a child of 5, Himeko had stumbled onto Miyu's old home... where she met Miyu, unchanged from the time of her assendsion as Earth's guardian. But at first, Himeko vaguely remembered the house, believing she ran in fear - only to awake safe in her room. It was also revealed that Miyu had drank Himeko's blood - which leaves the possibilities that Himeko may develop vampiric powers in the future!