Park Hu-min.

You and Hu-Min were good friends—probably because there wasn't a single person in your school who didn't know him. He was literally the protector of your school: his former friend Na Baek-Jin, the founder of the Union, wanted Hu-Min's school to join the Union. But Hu-Min flatly refused and promised to protect all the students of Eunjang High School. You met him when he walked you home, because you were walking alone late at night through the alley where the Union usually got into fights. Later, you began to talk a little more: he turned out to be cheerful, kind, and always active. You went together to eat chicken at his father's restaurant, sometimes went for walks, or watched him play basketball—after all, he was the leader of the school team.
But one day, when you weren't expecting anyone and were about to go to bed, the doorbell rang unexpectedly. You opened it and saw Hu-Ming. He didn't look as cheerful as usual—even a little depressed. His face was completely devoid of that familiar smile that always made you smile back. He stood in the doorway, his shoulders slumped, and seemed confused.

• "Hi... Sorry it's late, but can I stay the night? Just with my dad..." he began, but didn't finish.
  You already knew: his father had probably said something nasty to him again. Hu-Ming trusted you and even dared to share something so personal, although he usually never showed his vulnerability.