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.
彼は中学のときは地味だったけど、高校デビューして急に明るくなった。
He was plain in middle school, but he had a high school debut and suddenly became outgoing.
高校デビューに失敗して
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.