Rationale 1 – Kill or be killed.
Time dimension is very important in damage dealing. I think that part of the problem is that RPGs have always used constant damage. If damage becomes a function it varies with time and according to previous player (and probably enemy) actions. Linear damage increases… well linearly (2,4,6,8…) like every time you do damage its +x damage. Potential damage increases quickly each time (3,9,27,81…) thus being more effective in the long run. Exponential damage increases the fastest, but it can be balanced so it’s not useful always, or be used to trigger Limit Breaks. Logarithm is another kind of function that stabilizes after time, which can be of use according to the situation.
The functions are, of course, math functions so the concept and the rules are very simple, and most of us know them… but they are rarely used in RPGs. That’s what is showcased in the Dragon Quarter fight with Seiken (to the left in the graveyard).

Rationale 2 – Distributing damage.
When more than one factor is involved then damage distribution is important. A set of lenses can describe it as according to the lens a different effect will happen. The distribution also depends on the light, as laser optics is different that scatter light optics. The rules are the same for both kinds of lights but the results are different.
I also dealt with the issue of healing here by using polarized light. In the real life polarized light don’t heal, but anyway. Even if the party can heal it still depends on the optic rules, and as the lenses have to be changed it will also affect the interaction with the enemy. In that sense healing don’t erases previous actions, restricting exactly to its function: rising HP.
That’s what is showcased in the Lightness&Darkness fight with Pry and Chryst (to the top in the ruins).

Rationale 3 – Unlocking skills.
Yeah! Most RPGs have straightforward ways to unlock their skills. That may be good or bad depending on how it’s used. I think that powerful versions of previous skills are needed, as that solves the issue about damage over time. That’s why I put them even when it was suggested not to put “stronger skills versions”. Probably MP has become too abundant so at the end skills can be tossed endlessly. That’s why this system doesn’t use MP but enables the player to gradually get more powerful skills. If the player doesn’t use them, the enemy will kill him for sure, that’s why they are needed. But more important than that, elemental affinity may lock or unlock skills for other elements. Past actions of the player affect his possible skills thus setting the conditions for advantage or disadvantage.
That’s what is showcased in the L-flowers fight with Almadana (to the bottom in the house).

Boss Rush.
Normal fights are easy and flexible, as there are different ways to solve the puzzle battles. But for more challenge and a wiser use of the theories about the rationales above, I put a Boss Rush. HP is reduced and battles may be faster, thus making the player to think more strategically to overcome the damage (HP) over time (turns) issue that has been balanced against player odds.
That’s what is showcased in the Boss Rush fight with Vanesa (to the right in the threes).