Editing Breath of Fire

Note: For clarification, the 100% additional damage is 100% of your Attack stat not 100% of the damage of the attack used to trigger it and is counted as a separate attack meaning it can crit separately from the attack used to trigger it and damage is calculated separately from the attack used to trigger it. Certain Hypers have skills that count as regular skills, in these cases the skill will both activate Breath of Fire and trigger the follow up damage without needing a regular attack to trigger Breath of Fire's effect.

The main Hypers that optimize Breath of Fire are Strikers and Assassins, not to say that other Hypers can't use it. Since it scales off of Attack, you'll mainly want to build Attack and Critical Rate/Damage to optimize on its effects. And since it doesn't matter what skill activates it or triggers it, you can use it as often as you'd like. Whenever possible it is optimal to activate it before a fight and wait to use it, as the cooldown occurs as soon as a skill is used to activate not when it is triggered, meaning you can queue up Breath of Fire, use it and then have it available sooner.