bog, wetlands, used in proper names, (kokuji)
萢 is a kokuji (Japan-made kanji) that centers on marshy, waterlogged ground: a bog or wetlands. It is mainly used in proper names.
萢 is a Japanese kokuji, likely created by combining the grass radical 艹 with 泡 (bubbles/foam) to suggest a grassy, watery place like a bog.
Grass 艹 growing over foamy, bubbling water 泡 creates a picture of a soggy, marshy bog.
For やち, imagine a bog so thick that you yell 'YACH!' when your foot gets stuck: YACH -> やち.
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