The Protagonist is the main character of Devil Daggers and is the character controlled by the player. Nothing about their appearance, voice, or personality is known except for the appearance of their hand.
All that is known is that they came across the Dagger. They were then teleported to the Arena and forced to fight the enemies until death.
Probably it's very painful for a Protagonist to use a devil daggers when it's in a 3th state (after collecting 70 gems). Idea on this is coming from the fact that while shooting Protagonist is screaming, as his body is under huge stress because of being modified by gems and (of course assuming that Protagonist is a human) having to create this daggers from (probably) his own flesh, making him feel how he's riping his own body yo materialize daggers with which he can fight