Spoilers ahead.
This is one of the best youth k drama I have ever watched in a while. It definitely made me cry multiple times and the interactions of the two couples were so sweet. The message this show was trying to deliver is meaningful and touching.
The problem that I also face when I watch this show is also the pacing issues. not everything was concluded in the last episode and left with a lot of plot holes. For example.
Revolving Eun Yu and Segyeong:
How is the real Choi Segyeong doing in the US when Oh Eun Yu was impersonating her in Korea? How did Choi Segyeong and her husband's life change in 2023? Did Segyeong and Eun Yu's perspective and misunderstandings resolve? How is Eun Yu's fear of playing the cello and being the trophy of her mother resolve? Did Segyeong reconcile with Mr.Jonathan? Did Segyeong come back from US earlier?
(Since the real Segyeong was pretty much not really involved during half of the story, I really wanted to know how her life and perspective was changed despite not seeing the main characters in Korea during 1995)

Mr Jonathan and Eun Gyeol:
Did Eun Gyeol see him in the present? Did he not commit suicide anymore? Did he reconcile with his daughter?

Eun Ho ( I was kinda hoping he was a main character since he connected some of the dots of the story and he seems interesting but oh well):
What happened to Eun Ho and Eun Yu's relationship in 2023 at the end? How was Eun Ho and Eun Yu's relationship before the time slip? Is he still doing taekwondo?
(I'm sorry if you got heartbroken Eun Ho :( )

Yi Chan and Cheong Ah:(also with the rest of the band)
What happened to them after Yi Chan lost his hearing? How did they grow after that? Did the band disband?
What happened to the contest? What happened to grandma?

That's all. Thanks for reading my review xoxo. :3