it's highly likely that tav or endless could come along and answer this in a high society, blue-cheese manner but i'll field this one.

- the higher lulus magic stat is, the less spins it takes for one charge
- the weaker the magic spell, the less spins it takes for one charge
- as the number of charges increases, the number of spins needed for another charge increases (i.e getting the first few charges may only take 1 spin each while the next few will take 2 spins each and so on)

think thats it