How does the break mechanic work?

You can see the gauge on the enemy itself. Under the red health bar sits a gray one. That is the break bar, and it is the thing you are actually attacking when you bring a Break unit into a fight. Empty it and the target enters a broken state, its posture gone and its defenses lowered.

Break is a role, not a stat you build on any Aniimo. Break-role units are built for depleting shields and gauges and for disrupting an enemy's guard or poise. Magmarex is one of them. Whether you have a Break Aniimo on the team decides how fast that gray bar moves, which in turn decides how often the rest of your team gets a clean window.

Control states speed the whole thing up. An enemy sitting in a control state is easier to break with skills, and grappling is the simple way to get one there. The grapple pulls the enemy toward you and inflicts the control state, so the sequence of grab, then hit with break skills, is faster than swinging at a mobile target.

What the broken state is for

Broken enemies take significantly increased damage, and on bosses that means 250% damage while the break bar is down. The opening exists to be spent, not admired.

Ultimates are what you spend it on. Most ultimate abilities have a wind-up delay before they go off, so firing one at a mobile enemy wastes it. A staggered target cannot move out of the way, which is why ultimates are held back for exactly this moment. Charge attacks, the skills you hold down to build damage before release, have the same problem and the same solution.

Not settled: The 250% figure is stated for bosses. Regular enemies also take significantly increased damage while broken, but the exact multiplier for them is not pinned down.