Combat in Ar Tonelico is fairly novel, and it is a bit of a shame the designers did not do more with what they had.
Your party moves between screens on a dungeon map and enters random battles. This is actually a touch frustrating, as many games have moved past this system. I was actually hoping for something like SaGa Frontier, with the interesting and bizarre sprites appearing on the map; it would have solidified that nostalgic feel, and could have lent even more beauty and depth to the world by giving the empty-looking dungeons a populated feel. The one novel thing about the dungeon maps is the bar on the bottom right corner of the screen. It gradually shifts from blue to red, and the likelihood of encountering monsters increases as it changes color. After every battle, the bar decreases. Once the bar is emptied, no more monsters appear. This would be really interesting if only it emptied faster; in some dungeons, it just won’t empty at all. And its emptying rate doesn’t seem dependent on the difficulty of the monsters; beside that, if you return to an old area, you have to fight the weak monsters still. All of this could have been avoided with just a flag that prevented those monsters from spawning again. Also, there is no real benefit to emptying the bar, other than that the monsters no longer appear. It would be cool if you got some special prize, or that it unlocked a secret monster in each area. But there really is nothing.
Battles themselves can contain up to four party members. Normally, you will have three party members whom constitute the front row, and a fourth party member whom acts as the back row. There are five different party members whom can fill the front slots, and three whom can fill the back. Their roles are distinct. The front row members do regular attacks and protect the back row character, while the back row character supports the front row and can lay down devastating attacks. It is akin to having three fighters and a mage. The back row can be targeted only by special attacks, and in such a case, the front party members need to use a command to Guard the back row from damage, which in turn enables them to unleash a counterattack. It’s cool, but also a bit trite. You will always be able to effectively guard and counterattack. There isn’t much skill to it, unless you somehow let your party be so badly injured that the enemy could kill your front row characters if they do Guard.
The really novel thing is the Song Magic which the back row characters can use. The casters, called Reyvateils, choose from a limited selection of spells. The list includes a bunch of attack spells, called Red Magic, all of which appear to be non-elemental, and the only difference being their MP cost, their appearance, the rate at which they power up, and how much damage they can do. You can also cast Blue Magic, which are support spells. These can improve your elemental resistance/offense, your party stats, heal, revive, or absorb damage. Blue Magic seems to be the most tactically-sound option. Ironically, you can do more damage overall with Blue Magic, since you can make your front liners’ turns come up more frequently, and have them do more damage when that happens. Yes, Red Magic can become more powerful by attuning your party to an enemy (Just keep attacking an enemy, and a number will rise from 0 to 3 as you attack it), but you can still be more devastating with a good Blue Magic set-up. In either case, the longer a Reyvateil holds Red Magic, the more powerful the pay-off when the spell is unleashed, and the longer a Reyvateil holds Blue Magic, the higher the party’s stats rise. Reyvateils have an MP bar that drains, but by end game, the drain is negligible, and it refills very quickly when a Reyvateil is not casting.
The system would be a touch bland there, but it goes deeper. Grathnode Crystals, basically upgrades, can be installed into Reyvateils to power up spells, or anybody’s equipment, in order to power up the characters’ stats. Grathnode crystals have a rating of 1-4, which corresponds to the slots in a given spell or item. A higher slot can hold lower slot items, but not vice-versa, and there is only one slot for each. Furthermore, they have different ranks, from C to S, which determine their quality and overall usefulness. This has a variety of effects: for any character, you can have them add status effects to their attacks, and improve their base stats. For Reyvateils, you can also add more potent effects to their spells, other buffs, and make casting cheaper. This system makes characters distinct from each other, such that one character might specialize in having a massive attack, with every element doing 100% again of the base damage. Another character could specialize in crits. So forth.
The final major feature of combat is the series of bars at the bottom of the screen. A red bar grows right right to left, depending on how long a Reyvateil casts Blue Magic, or the devastation wrought by the Red Magic. Red Magic is much better at filling the bar, and even a very weak Red Magic spell will do so quickly. Did the designers mean for it to be like this? Probably not, because it means that Red Magic isn’t meant for doing damage: just for filling the bar. Anyway, on the left side of the bar is an empty circle. The circle feels when two conditions are met: the red bar is filled, and the bar below it is filled. The bar below the red bar consists of two bars meeting: a blue and a purple bar, from left and right respectively. These represent the front liners’ attacks increasing the blue bar, and the Reyvateil’s casting increasing the purple bar. When they meet, and the red bar is maxed, the circle is filled with a red dot, and another empty circle appears. This causes the Reyvateil to cast faster and unlocks better attacks for the front liners. You can fill up to three circles in a battle, at which point the party is devastating. This is not hard to do. Enemies can try to counter this by attacking, which drops the blue bar and may even remove a circle (which can then be filled again, but without the red bar requirement). However, their attempts tend to end in failure. The payoff is that the battles become easier, and the party gains more and better items when they fill more circles. Every enemy has guaranteed item drops of four grades, corresponding to the number of circles you have filled +1.
So, it is a complex system, but easy to understand and use. Once the player understands it, most battles become far too easy to win. Boss battles turn into stand-offs where the party just stands there, waiting as the Blue Magic causes the bar to rise and their stats to increase, occasionally attacking, until everything is maxed out, then finishing off the boss immediately.
And the enemies suck. Really, there are about eight different enemy models in the game, not counting bosses. I understand reusing sprites, but it is ridiculous how few monster models there are in this game. In this, different but similar models must be counted as the same. There is the bird. Then there is the somewhat bigger bird. And there are four different models of those two birds, which are really almost exactly the same bird anyway. It is trite, and end game battles do not offer much variety.
The greatest flaw of the battle system is that they never take full advantage of its promises. There are not monsters whom just steal MP. No monster acts so quickly that the party needs to have buffs up to effectively Guard the Reyvateil. There is rarely any need to switch between Songs. There is really only one type of Red Magic, and almost all enemies react the same toward being hit by it. Battles encourage party members to waste turns doing nothing in order to get the best result. Enemies can’t drop the current efficacy of the spells. It is a system that, were it more fleshed out, could have been amazing: as it is, it is just novel.