Kokkuri
This has got to be the greatest example of ateji ever: kokkuri, the etymologically onomatopoeic name for a table-turning-style divination game hugely popular in the post-Meiji Restoration period, spelt "狐狗狸": "Kitsune, tengu, tanuki".
What is interesting is, as Michael Dylan Foster points out in Pandemonium and parade: Japanese monsters and the culture of yōkai, is that
this association of the kitsune, tengu, and tanuki transcends the name of the game and comes to be literally embedded in the practice. [Early kokkuri debunker Inoue] Enryō's informant from Miyagi Prefecture, for example, describes the construction of the apparatus: "Into the bamboo rods insert tags inscribed with the words kitsune, tengu, and tanuki" [...] And in Ibaraki Prefecture: "Trace the characters on the underside of a tray with the tip of your finger, and cover with a cloth" [...] The inscription of these three yōkai endows the otherwise mundane structure with a supernatural quality. Operating through the principles of sympathetic magic, the graphs serve as metonymic representations, their presence a sort of lightning rod to call down the spirits they signify.
"This picture shows [each person using] one hand, but [in reality] both hands must be placed [on the apparatus]."
Leonardo Boiko:
Surely kanji work as symbolic, not metonymic, magic? Metonymic sympathetic magic would use tanuki hairs or something. A case could be made for pictographs as working within the law of similarity (Pierce’s “icon”), but…
Speaking of ateji, I just spotted a neat one in the ending lyrics for Tenkū Senki Shurato: 迷図 to spell メイズ。