Arcana Heart 3/Proration
Arcana Heart uses a proration system to lessen the damage of combos as you add up hits. The damage of a move in a combo is lessened based on the moves used before it with the first hit always dealing 100%. Each move has a unique proration value, and occasionally this value changes based on whether or not the move was used first in the combo. This system is applied on top of other damage modifiers such as guts and extend force.
Kira's 2A deals 500 damage and has a prorate value of 95(80). This means it has a first hit proration multiplier of 80% (.8) and a regular proration of 95% (.95) A chain of 2A's will do damage as follows:
First hit - 500 damage 100%
Second hit - 400 damage 80% (1 * .8)
Third hit - 380 damage 76% (.8 * .95)
Fourth hit - 365 damage 73% (.76 * .95)
And so on. So the formula for determining the proration multiplier for each hit can be summed up with a single equation.