1 when Nam si heon in 2006 in bus died or say coma here also, his soul time travelled in future to when koo Yeon Jun almost died with Tae ha nd was basically in coma nd he (Nam si heon from past) woke up their.
2 now after a lot of years when tht Nam si heon in koo Yeon Jun dies in plane crash his soul again transfers back to the one in coma (his original body) in 2006 its a loop that's why the timeline reset happened nd they all disappeared-both anomalies the Nam si heon who kept time traveling nd also future fl who kept going back n forth.
3 The past Nam si heon gave a choice to future Nam si heon in koo Yeon Jun body that he can survive this loop by not going in the plane which will crash but if he did than the unusual meeting of Nam si heo x Han Jun hee would disappear both from past nd future
4 hence why he chose to keep the loop ongoing. basically Han Jun hee finally decided to stop the loop nd told sml to destroy the catalyst the tape to reset the timelines that's why everything disappeared one by one in last ep.
Nd everything went back to its place.
There are two loops going on here one is ml going back forth on his side nd the Han Jun hee also going back nd forth on her side
1 The intervals for time traveling back nd forth are different for the leads.
2the ml always arrives their first way before nd meets to pursue fl nd dies in the plane crash nd goes back again.
3 now After the death of Nam si heon in koo Yeon Jun body nd almost a year passes then fl her own time interval time travel looping back nd forth.
The exact end description
The end here is
1 the time line getting reset as sml destroyed the tape as future fl asked him to
2 current ml nd fl forgetting everything nd going back to their own timelines and soon after they both also disappear as all their moments together disappear one by one.
3 Sml nd the introverted version of fl are together in the end in 1998 after timeline reset
4 Before the timeline gets reset ml promises the future version fl that he will find her no matter what
5 after timeline reset in future fl nd ml new versions meet again but they don't remember possibly but when they meet they get emotional without knowing why
6 it's indicated that they will be together in the end
