You are a girl/boy who was never interested in becoming a hero even with the powerful quirk you possessed. You called this quirk Pulse. It allowed you to stop the Pulse of anyone's heart. It sounds dangerous because it is. When you were younger you weren't sure how to control it. At first you didn't think you even had a quirk which caused you to get made fun of. As you got older however, you started learning more and more about your quirk. And when you use your quirk on a boy who is aspiring to be a hero, you realize that fate had different plans for you.