을 처음

… for the first time

→ 을
phrase Rare #32,351
… for the first time 을 marks the object of the action, and 처음 means “first time.” This pattern appears before an action such as seeing or meeting someone for the first time.
KO: 오늘 장관님을 처음 만나지?
EN: You're meeting the minister for the first time today, right?

오늘 장관님을 처음 만나지?

Is this your first time meeting the Minister?

— 순응자 (1971)