If unit's HP > 50% in combat against a lance user, unit makes a follow-up attack and foe cannot.
Breaker skills are some of the most specific passives available, with a separate skill for each weapon type (excluding dragonstones). The skill effectively lets the user negate and automatically win the speed battle against the chosen weapon type. A Breaker skill is well suited for patching up a single flaw within a team. If you have trouble with a green mage, G Tomebreaker allows a unit to easily cover that weakness. It’s also important to remember that Red, Green and Blue units cannot learn Breaker skills for colors effective against them (A red unit cannot learn Lance Breaker or B Tomebreaker). Swordbreaker is the most sought after skill for two reasons: sword users tend to have the highest speed stats, and are very commonly seen within the arena.
The most common use of breaker skills is on same-colour units: Axebreaker is mostly seen on Green units, and so on. This is because the majority of viable units already win vs. the colour they’re good against and lose vs the colour they’re weak to, leaving same-type units as the matchups that are most valuable. Anyone can benefit from a Breaker skill, but they tend to be rarer than Desperation or Quick Riposte, due to their specific nature. The best units for a Breaker skill are those with low speed, as they benefit the most from auto-winning the speed battle.
Attempting to KO a unit with a Breaker skill that counters you is rarely possible: Instead, try and finish off the enemy with a different unit. Swordbreaker is the most common, so if you’re relying on a sword user to KO enemy sword users, it’s a good idea to have a backup unit such as a blue in case you run into an enemy with Swordbreaker. If two sword-users with Swordbreaker clash, the effects cancel out, so having it on your own units can be a good answer.