You're right that it's an NPC, but it's not him.
Hint: The first two lines are connected, i.e. the speaker is taking umbrage at being called "vermin". Note that "vermin" should be taken literally here.
Repost:
What the hell did you call me?
Look at me, do I look like vermin to you?
You're gonna have to work to earn my protection now.
Nothing in life is free, after all.
How about we play a little game first?
Incorrect guesses so far:
Seifer Almasy
Gilgamesh/Alleyway Jack/The Four-Armed Man
Puck
Zidane's bedpost
Rachel
Freya Crescent
Amarant Coral
The NPC in the inn in Alexandria