I don’t exactly like this name, but I think it fits with the game.
You are a common villager who, instead of wishing to be a swordsman, a great hero for the people, just asked to be a hero. Then, he was cursed to only defend his own allies: he could use a sword to parry strikes, or a shield, or anything to defend himself, but if he was to attack someone, he will suffer the same damage he would cause.
This is a tactical RPG, with very short battles, that should last for two or three minutes: enough for the player to think about a strategy, see it work, or not, and get any rewards. As the player can’t cause damage, he’s best suited to go in front, attracting enemies and letting allies do the heavy work, or help them with special effects, a unique power of his. I believe the game game would use a system with five main powers, having one advantage, one disadvantage, and two neutral effects: it allows for faster battles, but also making the player able to fight without caring that much about effects and advantages.