What would Skill Refinery do?

Also complete upgrades like Defiant to Brazen, Bond 4 maybe? Not sure exactly which it would be but it's a nice change. Hopefully Guard 4 just works always

I’m pretty sure Mr.Pizza came up with a similar concept to this..

My big concept (an original idea I am proud of as Skill Refinery) was to have older units upgrade skills.

The example I've used is Lucina, who as OG has Defiant Attack 3, and Spur Attack 3. I say she and only she (maybe? or maybe it's okay to inherit) can upgrade Defiant Attack 3 to Brazen Atk/Spd (or something similar). And Spur Attack 3 to Spur Atk/Spd 2, or even Odd Attack Wave, or something similar. I've been trying to spam IS in the feedback section with this idea. It'll revitalize old characters, and at the same time provide other options for fodder (albeit expensive as 5* exclusive).

Of course, goes without saying about DB4, Rally Atk Up+, and others which already exists.

How about a feature where characters with exclusive skills can pass it on to other previous versions of themselves? Kinda like how certain units have evolved weapons like Siegmund to Flame Siegmund, but with skills.

PoR Ike gets Radiant Aether
Vanilla Hector gets Ostia's Pulse
[Big maybe] Fallen Celica gets Double Lion (That skill on normal Celica would be way too overpowered in her current state.)
Black Knight gets Warp Powder
Ephriam gets Solar Brace
Young Tiki gets With Everyone!
Etc.

Of course, this would likely cost quite a bit of Dew and Medals, but I think this can work.