expression, ichidan verb
become enthusiastic; get carried away; have a crush on
Idiomatic expression meaning to become passionate or obsessed about something or someone. Often used for romantic crushes or intense hobbies.
彼は最近、新しいゲームに熱を上げている。
He's been really into a new game lately.
彼女はクラスメートにすっかり熱を上げてしまった。
She's completely fallen for a classmate.