This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 鼲 is uncertain. It combines 鼠 (mouse/rat) with 軍, but the original semantic or phonetic role of 軍 in this character is unclear.
With no clear meaning, picture a mouse (鼠) wearing a tiny military helmet (軍) — a strange, uncertain creature.
For コン, imagine a con artist mouse (鼠) trying to join the army (軍): con -> コン.
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