Well.
Forsaken Statue work of this way.
Example: You are going to upgrade from level1 to level 2 Phantom Tail, you will need 2000 FS, After you land they first strike, a circle of the weapom element(Fire and lava for this one) and stop enemies from attacking you(but you still suffer from fire, a highter level of upgrade will mean more DoT).
Eacht time you strike, you infuse the statue with FS, you will need to get a A combo rating to destroy the statue and upgrade(Level 3 will demand a SSS!).
If you ran out of FS and you havent destroyed the statue, it will drain your heal bar, and leave you without FS(I want to make upgrading weapom difficult, otherwise players will get everything too easy).