fairy
佺 centers on a supernatural being: a fairy or immortal spirit. The given meaning is narrow, so treat it as a rare character for a mythical creature.
佺 combines the person radical 亻 with 全, which likely contributes the sound. The exact historical development is uncertain, but it is probably a phono-semantic compound for a type of immortal or fairy.
A person 亻 who is whole 全 and perfect, like an immortal fairy untouched by mortal flaws.
For セン, picture a thousand (千, せん) fairies dancing around a perfect person: 千 -> セン, and the fairies are the 佺.
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