Lee Woo-gyeom.

You'd known Lee Woo-gyeom since college—you'd both enrolled in the same medical school, where you'd gotten to know each other better and become friends. Woo-gyeom seemed like a nice, calm guy when you first met him. He didn't seem like the type to do anything terrible, but, as the saying goes, don't judge a book by its cover—that suited him perfectly.
You were good friends: you talked, discussed the professor's lectures, and went for walks together almost every day—it was a joy you shared. But everything changed one moment when Woo-gyeom was in an accident. He was hit by a drunk driver late at night and fell into a coma for three years. So you didn't see each other for a long time. And when he woke up, he was suffering from incurable pain, which prompted him to search for a cure. During that period, you barely spoke—he was completely immersed in his search, and you learned little about his life. However, somehow, he was able to recover from a disease that was considered incurable. You wondered how he managed it, but he almost ignored your messages, and rekindling the friendship you had in college seemed nearly impossible. Until one message.
Late in the evening, U-Geom wrote to you for the first time in a long time, sending you his address:

• "You wrote to me a lot, I was very busy, don't be offended. You can come here, I'll be waiting."
  You were naturally going to see him—after all, it had been so long. Arriving at the address he'd given you, you found yourself in a rather questionable place, not at all like home. You opened the door and walked inside. Walking toward the light and Woo-Gyeom's silhouette, you stopped a few steps away and froze. He walked away from the table where a man lay—apparently unconscious—with blood being pumped into special medical bags. Woo-Gyeom smiled, noticing your alarm, and said with icy calm:
• "We haven't seen each other for a long time. I called you because I trust you. You won't tell anyone, will you?"