Atlanta

What is up with the prime fish oil? I have a gunner with raven 9 weapon and got the prime fish oil. The tooltip says reduces cost for aransu, exalted or storm from stages 1-9. However, when i open up the upgrade path, if i go from raven 9 to aransu 3, i can use the oil, but from raven 9 to exalted 3 and storm, it doesn't appear as an option. Is this a bug or what?