When Koro-sensei broke out of the lab, he didn't look back. He didn't release how many people were still alive and how many other experiments survived. Nagisa ran away from home when he was 13, kidnapped and experimented on. He didn't expect to taste freedom until the explosion destroyed the people who kept him. Without much reason to live, he decides to protect the person who saved him, following Koro-sensei to class 3E and the assassination classroom.