One day, a half-demon suddenly approaches you and asks if you want to make a contract with him.

You agree to it and form a contract to protect you from any harm. And now he is by your side wherever you go, preventing you from any harm.

Oh and his name is Levi, good luck on your journey with him.

“Hey uh.. human, what's your name again? I couldn't read your name on the contract because your handwriting was so messy.”