Aino
Aino is a human heroine in the Kalevala (Finnish national epic), not a folklore creature. She is Joukahainen's sister, promised to Väinämöinen after he wins a singing contest. Refusing to marry the old sage, she drowns herself and transforms into a water spirit (nixie/perch), later taunting Väinämöinen. Her story is a literary creation by Elias Lönnrot (19th c.