Tradition: Japanese Mythology
Alternative Names: Mosquito Spirit
Category: Insect
The Myth
Ka-sei is a mosquito spirit that can transform into a human and disguise itself as a sumo wrestler. It appears in the Kyogen play Mosquito Sumo, where it comes from Moriyama in Ōmi Province, a place associated with mosquitoes. Taking advantage of the popularity of sumo wrestling, the spirit travels toward the capital in search of employment, intending to drink human blood.
The spirit encounters Taro Kaja, a servant tasked by his daimyo with finding a new retainer. Believing the stranger to be an ordinary sumo wrestler, Taro Kaja brings him to his master. The daimyo is delighted to discover that the newcomer is a wrestler and immediately challenges him to a match. However, the supposed wrestler moves with a buzzing, flying motion, making the daimyo dizzy and causing him to fall before he can touch his opponent. During the encounter, the mosquito spirit also bites him and sucks his blood.
In the Ōkura school’s version of the play, the daimyo eventually realizes the stranger’s true nature and devises a plan with Taro Kaja. During their next match, Taro Kaja uses a large fan to disrupt the spirit’s flight. Unable to move freely against the gusts of wind, the mosquito spirit is caught by the daimyo, who pulls out the stinger that has emerged from its mouthparts. Defeated, the spirit staggers away.
The Izumi school’s version ends differently. Although the daimyo initially manages to defeat the mosquito spirit with the help of Taro Kaja’s fan, the spirit throws him again while he celebrates his apparent victory. Having ultimately lost the match, the daimyo angrily throws Taro Kaja to the ground instead.
On stage, the mosquito spirit is represented using a mask called Usobuki or Usofuki, which has a narrowed mouth, along with a costume resembling mosquito wings. During the sumo scene, a long, thin roll of paper is inserted into the mask’s mouth to represent the mosquito’s needle-like proboscis.
Sources
“Ka-sei.” 新版TYZ 妖怪図鑑 (New TYZ Yokai Encyclopedia). https://tyz-yokai.blog.jp/archives/1070069162.html