にあう
to suit, to match well
The thing and the person resemble each other closely enough to fit together. The same nearer に as 似る and the same あう as 合う, and the kimono looks as though it were made for her: にあう.
似る にる is looking like something. 似合う is looking right alongside it.
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Emaki is not affiliated with, or endorsed by, Kaishi 1.5k or its authors. The word, reading and meaning come from the Kaishi 1.5k deck, used with their permission. The mnemonic, the note and the kanji breakdown are original work, published under CC BY-SA 4.0.