I don't watch shows until they are completely available to watch. I've been burned too many times by sad/terrible/rushed endings. I skulked around daily under the comments for this show, reading everyone wax eloquent about how wonderful it was. That's normally the kiss of death for me. If everyone thinks it's the best thing in the world, I'm usually meh about it. Then, add to that my aversion to time travel movies (they always raise more questions than answers for me) and that this sounded exactly like Back to the Future, I wasn't holding out much hope. My hand is raised here, I admit it, I was wrong.

I won't reiterate the storyline, but I will say this didn't reach out to me as a romance so much as a family/friend-fest. I didn't even feel that the focus was so much on the school aspect of it, but the kids themselves, which I loved. This show had so much heart. I laughed a lot, I cried quite a bit, and I vacillated back and forth between "hurry up and show me what's going to happen next" and "slow down, because I really want to savor this." The story was great, but the characters themselves, and the actors portraying them, were what kept me coming back for more. I really liked the direction they took with two people going to the past, one to save a life and one to end a life.

Ryeoun as Ha Eun Gyeol. This was a teenager that was old for his years, by necessity, as he was the mouthpiece for the whole family. That's a lot of responsibility to have from a very young age. Ryeoun was excellent, and I felt his wonder at meeting his younger father and finding him completely different than he imagined. Most of the scenes that made me cry involved Eun Gyeol. He was trying so hard to make things right, time after time. I could feel his desperation, as well as his sense of being unsuccessful. This story arc spoke a lot to destiny - are certain things that happen in our lives fixed? If you change something in one direction, does the river of destiny re-route itself to make it happen anyway?

Choi Hyun Wook as Ha Yi Chan had the gangly puppy/bouncy behavior going for him, moving from one thing to another quickly. If you are going, you run, if you are talking, you yell, if you don't know how to react to someone, you put them in a headlock. He was very immature, which was a perfect foil for Eun Gyeol, who had to switch places and become the father in the past. I did struggle with the length of time that he liked Sy Keong, so when he switched to Cheon Ah, it was kind of sudden and didn't necessarily flow well.

Seol In Ah as Choi Sy Kyeong/On Eun Yu. I had difficulty with this character. First, her voice is so distinctive, I kept flashing A Business Proposal when she talked. Other than that, my difficulties were more character related. Eun Yu was a totally repressed young woman, being driven by her mother's wishes. I don't feel that she would have been able to have the personality change that she did in the past. And, to me, there was something not always very nice about her, like she thought she was better than everyone else. And we didn't get to see any difficulties with her adapting to the past.

Shin Eun Soo as Yoon Cheon Ah. She was the standout for me. Eyes wide with sadness, living in silence, being betrayed by those that were supposed to take care of her, the character of Cheon Ah had a strength about her. I was so glad they didn't make her a doormat. It is really hard to act without using your voice, and Eun Soo was wonderful.

Go Doo Shim as Lee Chan's grandmother - she was terrific. She surrounded herself with students, cared for everyone and kept everyone fed. I love how she didn't baby Lee Chan, but was raising him to be a responsible adult, supporting him in every way she could.

The band mates were fun to watch, full of pen-up energy, running here and there. It was like they were all amped on caffeine, then I remember that's what it was like as a teenager. The Master was mysterious and brought levity to a lot of the scenes. I loved when he'd throw random English words in. Cheong Ah's step-mother - don't even get me started.

The soundtrack was very good and, of course, went along with the theme of the show.

BONUS - the lengthy BTS reference was a hoot!

Small nit-picky things:
I would have liked to have seen Yi Chan and Cheon Ah together for a longer period of time in the past, and watch their relationship develop.
So much bullying by so many people. And what about Yeom Byung Ho and his mother? They made a big deal about them and then they disappeared.
All the past band members, in 2023, thought Eun Gyeol "looked familiar". Did everyone get amnesia or something?
It was very vague as to whether his father remember him from the past as well.

Bottom line? Watch it!