There are some "really" empathetic people around here...
I'm not saying you have to like her or that what she did wasn't wrong, but you can understand why she did it and not think she is some kind of evil witch that deserves all the worst things in the world.
1. She is adopted. Her adoptive father's factory went bankrupt when she was in third grade. Not explicitly said, but implied, her mom started overworking herself to keep the family afloat.
2. She was disliked by many (?) in her middle school because she kind of looked like a beggar. I mean, her family was probably drowning in debt, barely affording rent, food and utilities. Who knows in what kind of apartment they where living in.
3. Her adoptive mother died from overwork in her first year of high school (Info from chapter 19, just like the point 1 and 2). Before her death, Mia begs Taesoo's mother (who is also a friend of Mia's adoptive mother) for help. Taesoo's mother accepts, but asks Mia to spy on Taesoo. This is the part that made a lot of people angry, but what were her other options? Start working part time? Sure, but can she pay the hospital bills with just that? When she also has to pay rent, utilities and food? And her father is throwing the money that was supposed to be used for medical bills out of the window and drinking himself to death? Ask Taesoo for help? When she knows he had a strained relationship with his parents and doesn't have money of his own? Sure, it's not morally correct, but was she just supposed to not do anything and just see her mother die?
4. On her second year of high school, her adoptive father forces her to leave the city/town they where living in (I'm guessing to escape the debt collectors or something. Info from chapter 1 and chapter 19). This also annoyed a lot of people. Sure, she could have written Taesoo a message saying, "Yo, my father is skipping town to escape the debt collectors, so we gotta bounce. Don't have time to tell you in person, but this is goodbye"? After she took money from Taesoo's mother to help pay for her mother's medical bills? And she was what, 16-17? Sure, she should have, as that was the best for Taesoo, but you can also understand why she didn't. And if you can't, you have no empathy. She didn't willingly disappear, but she did choose to not tell him anything.
Seojin told asked her why she hadn't told him about her amnesia/mental problems and Seojin gives the most likely reason for that which is, "She doesn't want Taesoo to pity her." Seojin never said, "Gurl, you gotta seriously explain him why you skipped town back then. Like, omg, seriously. You have to." She wants Mia to realize that she has feeling for Taesoo. Yes, we already know that Mia already knows it, but Seojin doesn't.
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You can like Heesu, you can like Nayoon, you can dislike Mia for the mistakes she has done, but please, have some empathy. She did what she could to survive. Sure, she made mistakes, but she never was like, "Yes, let me collude with the evil mother to have Taesoo royally screwed." She felt really guilty every step of the way. That's also what made her situation worse. If she had had thick skin, she could have asked Taesoo for help, even while know his relationship with his parents wasn't the best. She could have asked him for help after she disappeared and he probably would have helped however he could. There are a lot of things she could have done, but didn't, but that doesn't make her an evil person you should hate.
I know the people that are angry at her will never read all the way here, but if you do. Good job. I hope you can be a bit more empathic in the future. Just a tiny bit.
