being a fan of; being a supporter of; pushing for
one's favourite (member of an idol group, character in an anime, player in a team, etc.)
推しのグッズを全部集めた。
I collected all my favorite's merchandise.
推しのライブに行く予定だ。
I plan to go to my favorite artist's live show.
推しが卒業して寂しい。
I'm sad my favorite graduated.