large mythical fish, roe
鯤 centers on a legendary giant fish, often described in Chinese mythology as a creature of immense size. The roe meaning is a specific extension, referring to the fish's eggs.
鯤 combines 魚 (fish) with 昆, which likely provides the sound コン. The character originally referred to a mythical giant fish in Chinese legend.
The fish radical 魚 on the left tells you it's a fish, and the right side 昆 (which can mean 'multitude' or 'swarm') hints at something huge or abundant. Picture a fish so large it could swallow a whole swarm of smaller fish.
For コン, imagine a giant mythical fish named 'Con' (like a con artist, but huge) that tricks sailors by pretending to be an island. Con -> コン.
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