Kasa (a Touhou LW original) refers to the halo that appears when thin clouds pass over the sun or moon. It is a ring of light in the sky that looks like a white rainbow. The way this ephemeral phenomenon appears next to a bright light, as if by magic, makes it a fitting temperament for Akyuu, the Child of Miare. Akyuu is endowed with Wood Phase, with her duty to record her memories on paper, and Moon Essence, with the Child of Miare's cycle of reincarnation after death. The strong and kind Wood Phase resists Water Phase, because water nourishes wood, but it is weak to Metal Phase, because metal carves wood. The cooperative and indecisive Moon Essence resists the alluring and arrogant Sun Essence, but is weak to the diverse and uncooperative Star Essence.

Akyuu's ability is to remember and never forget anything that she experiences. This is also known as having a photographic memory. This ability has apparently been passed down through all the Child of Miare incarnations starting with Hieda no Are. Akyuu uses this ability to compile various books, the Gensokyo Chronicle being chief among them, and also sometimes acts as the secretary for meetings between religious leaders. However, she also appears to suffer from having to remember things that she'd rather forget. The Child of Miare appears to lose almost all of their memories when they reincarnate, so you could say that the Hieda house's large private library is their external memory repository. If any of the information stored in the Hieda house's library was tampered with, it would also tamper with the Child of Miare's memories and thus the Memory of Gensokyo itself... The retainers of the Hieda house bear a huge responsibility.