It's not uncommon for RPGs to have some sort of mechanic that unleashes a strong move after a certain meter fills up or something similar. Final Fantasy X, for example, has Overdrives. This was a bar that filled up with various means, and once filled, the character could do a strong move in battle.

Untold Story has it's own idea of this mechanic: Decisive Skills.

There are many forms of Decisive Skills (called DS from now on). The most basic is the Level 1 and Level 2 DS, which every main party member will have. The picture above is Rover's Level 1 DS: Skill Recharge, which will restore any ally's SP by 50% of their Max. Every character will have their own unique Level 1 and Level 2 DS, though the Level 2 one must be unlocked during the game.

There are three types of DS: Restoring, Buffing/Debuffing, and Damaging. Rover's Level 1 was restoring, while Drake's above is damaging. Buffing/Debuffing DS will either boost a character's stats, or decrease the enemies. Damaging ones will simply deal damage to the enemies.

Just as there is HP and SP, characters also have DP, or Decisive Points. This points are how characters will preform their DS. Level 1 DS will always cost 50 DP, while Level 2 DS will cost 100 DP (100 is the max amount that can be obtained).

In general, the only way to gain DP is to take damage in battle. The more damage taken per hit equates to more DP gained. A mortal blow will generally fill up the bar quickly. DP is not retained after battle as well, instead being reset back to a small amount at the start each time. However, some pieces of equipment can change these bases. Some equipment can grant DP for free each turn, regardless of being damaged or not. Another special accessory can retain DP after battle, allowing the character to maintain their stock to unleash a DS at the beginning of battle.

There are more DS that just Level 1 and Level 2. Around the world you will find items called DScrolls. When used, these items will teach one of the main party members a special DS. For example, the Rejuvenate DScroll will teach a character the Rejuvenate DS, which will restore the user's HP and SP by 25% of the max value.

As seen, the DS from the DScrolls cost less than the standard Level 1 DS. This allows the player to decide to use a DS now, or save up for a stronger Level 1 or Level 2 one later in the battle.

It should also be noted that there are a limited amount of DScrolls in the game, so not every single party member will be able to learn every DS. It is up to the player to decide which DScroll goes with the character they want to use it most. There are no right or wrong answers, so pick whichever fits your strategy best.