high school debut; reinventing oneself upon entering high school
Colloquial, often derogatory. Refers to someone who changes their appearance, personality, or social behavior when starting high school, usually to become more outgoing or popular.
He was plain in middle school, but he had a high school debut and suddenly became outgoing.
My high school debut failed and I ended up not fitting in with the class.
Compound of 高校 (high school) and デビュー (debut, from English). The term describes the phenomenon of students using the transition to high school as an opportunity to change their social image.