Combine water and anchovies in a saucepan; bring to a boil and cook for 10 minutes. Remove and discard anchovies; set anchovy water aside.
Combine chile paste, sugar, soy sauce, and corn syrup in a bowl.
Add rice cakes, onion, and chile paste mixture to anchovy water; bring to a boil and boil for 5 minutes, stirring occasionally. Add spring onion; boil 3 minutes more.