Complex sentence: Unlike his gloomy image in school, Izumi's look outside school would have easily gained him popularity with his pretty face but he hides it under glasses and grows his hair long to hide his ear piercings.
Split into simpler sentences: Unlike his gloomy image in school, Izumi's look outside school would have easily gained him popularity with his pretty face that he hides under glasses. Izumi grows his hair long to hide his ear piercings.