I've seen seen and read enough stories of a teacher taking on delinquent class and going through the trouble of changing the kids like Gto, Rookies. So it felt a bit boring to me. But it's Donnie Yen, so give it a try.
Min Ah treating Gi Sup as her brother was really cute. Really enjoyed watching it. Don't get disappointed just because it has no romance in it. It's a heartwarming sis-bro relationship u will come to appreciate.