Based on Edo-period records and regional folktales. An aged char trout appears in the guise of a Buddhist monk and speaks to anglers. It often urges moderation, citing the temple’s domain or the pool’s lord, and departs quietly if given alms. Later it may be caught as a great char, where rice or rice cakes given as alms are found in its belly, revealing its identity. The motif reflects reverence for river and pool guardians and ideas akin to eel and other water deities. Depending on region, it appears as a harmless, didactic type, a warning type bearing deadly poison, or a salvific type that sacrifices itself to stop a levee breach, yet all embody folk norms that safeguard the boundary between waters and livelihoods.