2017: GOOD DAY, The Unit
Later that year, she became a contestant on KBS 2TV's reality survival show The Unit. She was eliminated in episode 13 after ranking 29th place.
November 13, 2019, Sunn was introduced as a member of C9 Entertainment's next girl group, Cignature. They are now managed by the subsidiary J9 Entertainment.
Sunn had not posted on cignature's SNS since the 17th of March, 2021. Along with Ye Ah, she opened up her personal Instagram and they were the only members to not post about Semi's birthday. She does not follow cignature on her Instagram, unlike Ye Ah. It was confirmed on the 27th of April that Sunn and Ye Ah had left the group in preparation of a comeback.