Hata no Kokoro is a youkai called a menreiki, which is a tsukumogami of old masks. She appears to be a human, but her true form is that of many masks. Her masks come from Hata no Kawakatsu, the forefather of sarugaku from which Noh and kyogen can trace their roots.

Each mask that Kokoro owns has its own emotion attached to it. When she dons her masks, she takes on that emotion, and it also affects the people around her. She can display a wide variety of emotions with these masks, including happiness (the god of happiness and old man masks), confusion (the monkey mask), and anger (the Hannya mask). She has a total of 66 masks in her possession.

Noh started in the Muromachi period and has over 600 years of history. It is a long-held customary form of Japanese theater. The words, intonation, and melodies used are said to keep the Muromachi era tradition alive in modern times.

Toyosatonomimi no Miko says that she made Kokoro's masks. Kokoro lost her Mask of Hope, which Koishi says she later found near a fissure. Could the geyser eruption have something to do with it?

Kokoro can often be seen performing Noh at Hakurei Shrine. It is said that it helps her maintain her mental state. Her typical audience comes from the Human Village, so full-fledged Noh would be too difficult to follow. So, Mamizou worked with Kokoro to make an easier-to-follow performance, called Shinkirou. This kagura, a dance as an offering to the gods, has been a roaring success.