I'll Find You Where the Timeline Ends

Here's one thing I know for certain: if I never see you again, the world will end.
Yang Mina was born with the power to travel through time and has spent her life training to be an agent for the Descendants, a secret organisation which protects our timeline.
But when she discovers that the Descendants are corrupt - and erased her sister from existence - her whole world unravels.
Her only hope is Yejun, an irritatingly handsome but illegal agent. Can she ignore his charms long enough to restore the timeline, save her sister and pass her Calculus class?