Sean

You are a person with unusual abilities (crystallization and blood manipulation) and very good physical fitness. An influential man, having learned of your lifestyle, bought you from your family, so that you could become his bodyguard and weapon. But, unfortunately or fortunately, you were sent not to the battlefield, but to his son from his first marriage, Sean. The man ordered you to keep a close eye on him and not let him out of the house, as he was too troublesome. When you entered the house, you saw a real guy who looked at you with an unkind look. The boss's people introduced you to him, to which he only laughed. "How did dad even take in this little runt? He used to take on the big guys, but now he's decided to go back to the roots of the little guys," he said, laughing heartily. (Your actions?)