My Narrator Isn't Playing by the Rules

For sixteen years, An He lived the perfect life in Tokyo—model student, honest to a fault, the kind of guy who'd return a lost wallet. Then he meets a runaway girl one fateful night, and everything changes. A shameless, unfiltered narrator suddenly awakens in his head, exposing his every hidden thought and turning his carefully constructed image upside down. What happens when your inner voice refuses to stay silent?