은/는 (après -까지)
mark contrast on a time boundary
Form
Time expression + 까지 + 은/는. Here: 만나기 전까지 + 는 → 만나기 전까지는.
Function
은/는 turns the period “up until before meeting Taehyung” into a contrastive frame: Sara thought that up to that point, and the situation changed after the meeting.
Why this form?
-까지 — “until / up to”: marks only the time limit; 만나기 전까지 그렇게 생각했어요 is grammatical, but the before/after contrast is less foregrounded.
-까지도 — “even up to / still up to”: instead emphasizes that a state continues or extends as far as a noteworthy limit; -까지는 here contrasts the earlier period with what follows.
How to build it
은/는 can attach to an adverbial phrase already marked by 까지. Since 까지 ends in a vowel, 는 is used.
Forms not to confuse
-까지
졸업하기 전까지 여기 살 거예요. — I’ll live here until before graduation.
-까지도
마지막 순간까지도 포기하지 않았어요. — I did not give up even up to the final moment.
Examples
저도 태형 씨를 만나기 전까지는 그렇게 생각했어요. — I thought the same until I met Taehyung.
어제까지는 괜찮았어요. — It was fine up until yesterday.