Restores HP=7+this unit's suffered damage. Unit heals HP=half suffered damage. Slows Special trigger (cooldown count+1).
Martyr is one of the more complicated healing skills within the game. It is the only healing skill to have a HP condition on the user, healing more the lower the HP of the user is. Martyr is tricky to use thanks to it's HP requirement, but also comes with the added bonus of a Live to Serve effect. It means the user can sustain themselves without running Live to Serve and can instead use their B slot skill on Wrathful Staff, Dazzling Staff or a Chill skill.
Using Martyr assumes that the healer themselves will be taking damage during the round. This means it is only suitable for healers with some defensive merit, with either high Defense or Resistance. Having Reciprocal Aid on an ally can be useful when using Martyr, to let an ally transfer damage to a healer without actually having them enter potentially dangerous combat.
Unfortunately, Martyr's HP condition is difficult to activate. Healers tend to have low combat stats and even their offensive builds revolve around protecting themselves from taking damage. In addition, the HP restoration effect is detrimental, as it will reduce the healing output of the user. Being only useful on a few units, It can be better to skip Martyr for a more reliable healing special.