aw, it was a good idea to address the problem of heavy school bullying - but sadly not the way it was done here -
here is why:

what is good about it:

1. some few actors are good (especially some older side characters), the younger leads are ok - at best.
2. the storyline sounded promising
3. the soundtrack is rather good and fitting the topic

what is bad:

1. well, the main problem for me is reality. So the female lead shows us in 2022 what she does when she gives extra tuition to a bratty youngster. He verbally gets quite offensive, she listenes to it and then - tada - gets out her cellphone and tells him it's all been recorded, his mum heard it and this was his last lesson with her. So in the very first or second episode she shows us what anyone with half a brain cell would do in such situations.

So, we then get to see our female lead as a teenager at school and some really awful torture scenes of school bullying,

(that is my point 2 by the way, there was no need to show these scenes so excessivley, it had quite a touch of torture p0 rn which addresses the very wrong audience...to get over the message what happened to the poor girl a third of the scenes would have been way enough)

we fast forward to the year 2022 again, when our female lead has forged her revenge plans for years and finally gets to be the teacher of her arch enemie's little daughter. (I here do ask myself though how would a girl coming from her background with no parents, bodily heavily disfigured and traumatised, with no money and no connections get into college alone and study to become a teacher?) But I see the point that this is supposed to be a revenge story so let's get on.... all that happens then is nonsense. Her former torturer is now obviously very rich, (which lets me question by the way why a very rich person would send her daughter to the same school she was in together with our female lead, a very poor kid? Wouldn't a rich woman send her precious daughter to a private school, especially in South Korea?), our lead becomes the teacher of her little daughter and then - threatenes her verbally several, many, many times openly? Why would her enemy not simply tape all of the open threats ('you need to be punished and I will punish you' etc). She is rich and certainly has influential connections, so why would she let this go on for a single minute? Also our female lead tells her she should 'not dare to take her daughter out of this school' - well, why would she not do that? as she simply can?

So this whole revenge thing gets absurd as in the way it's shown it simply would be impossible. What would happen in reality is the rich woman, espcially one as cold blooded as this one is shown, would tape her threats, go to the cops, use her connections and either get our female lead arrested or even worse.
Also, if the police would find her room with aboot a thousand photos and news articles about the woman, they would certainly call her insane and obsessed and would take claims of threat against the woman and her child even more serious. Even if our female lead would then claim all the wounds on her body were inflicted by that woman in their teeager time? She would have no proof, and with the obsessive photo room the police would declare her dangerous and insane and claim she is just obsessed with the beautiful weather forecaster on TV because she herself didn't make it far in life, and she probably always has been jealous about the other woman, even back in their teenage years.

3. the dialouges were mediocre at best. The whole 'romantic' storyline with the young doctor? Didn't work for me. No chemistry, and the dialogues were horrid and seemed artifical and forced many times. (Especially in that scene in the park, where he asks her a concrete question and she suddenly starts to talk pseudo-poem stuff about the snow and whatever else) Also the whole storyline with these two seems so 'created' and not real to me.

4. Compared to other dramas with heavy content I found the acting ability of the leads rather bad to be honest. The bullies as adults were too overdrawn, they didn't seem like real people to me. Same reasons, artificial dialoges, speaking too loud or even screaming, some scenes looked like rather bad school theatre to me.


Conclusion:

a good idea to address the topic of school bullying - but not like that? You simply couldn't take revenge like it's shown here for at least 5 different reasons, most importantly because the possibility of taping and nipping all the great revenge plan in the bud.
It's more like a juvenile revenge fantasy, not thought through to any end. having immature fanatsies about revenge is just that - immature and far from intelligent. But as least for me, it has to be an intelligent, thought through story, otherwise it's more like playing ego shooters, no brains but what a satisfaction with brains off Oo
Disappointing.