the drama's story is not the best, but it could be a lot better if the script was better. the main couple (nabi and jae-eon) are literally the most boring characters, even so the side characters have more charm than them. nabi, initially, looks sane and all, but she's just SO confusing. to the point she looks kind of dumb, really dumb. she says to herself that she will not fall into jae-eon's tricks and later she changes her mind when he kisses her. there is no reason to why she likes him, he literally does something nice for her sometimes and that's it. his character is really annoying and touched her all the time, even when they just met, and it was a bit hard to watch them together because she looked too shy and uncomfortable. she knows that he's not committing to any closed relationship and it's sad about it, she knows he can't make her happy and still decides to stay with him at the end. he did a lot of bad decisions throughout the drama and said some manipulative things as well. at some point the two were unbearable to watch, they had no chemistry besides their physical attraction to each other. she just likes him because she finds him attractive, even though he's kind of a jerk and has no personality (except his quirky character trait of liking butterflies). she rarely looked really happy when she was with him, always with a distressed expression worrying if he's worth it. i don't understand the point in dating someone if you'll be worrying if they're a good person or not all the time and doubting them.
the good part of the show is the side characters. they have interesting and dynamic personalities that go well together and creates great chemistry. bit-na is very outgoing and social, she knows everyone. sometimes she was annoying but it's normal to have some defects. her actress made a good job incorporating the character. her boyfriend was ok too and they looked cute together (mainly towards the end). now, sol and jiwan; they're the best couple in the show, in my opinion. they're really cute and they seem really close (the actresses had so much chemistry and it didn't looked forced at all). their relationship is simple and adorable, and i liked pretty much every dialogue they had. sol was cute in every scene, her character is chill and she looked really natural all the time; she was kind of oblivious but it was cute. jiwan could be annoying sometimes but it's just the way she is, and she's really funny; sol likes her this way. their way of showing affection had me crying. sol is very subtle and kind, but she was always thinking about jiwan and doing something nice for her, even if it seemed small (getting her a plush of the character she likes, getting her candy, wrapping her with the blanket on a restaurant). she was just naturally attentive towards her. jiwan was always leaning towards her, too; but she showed it hugging sol and always taking care of her (even if it didn't look like it), she was easily jealous too but it was because she didn't know how to deal with her feelings for sol at first and was confused about it.
the other couples are fine too, the couple with the ones who both had glasses were so funny and really seemed like they were married. they had more chemistry and personality than the main leads.
to sumn-up, this drama was very hard to watch when the main characters were together on screen. it just got boring and they never had a great dialogue whatsoever. but when the side characters were on screen, it was very light-hearted and nice. do-hyeok and the other guy who also liked nabi were cute and they should've ended up with her, she was not as boring as she was with jae-eon.
also, towards the end, when jae-eon free his butterflies, i thought it would be a metaphor for him leaving nabi alone and acknowledging that he's not the best partner for her. but it was not and it was really just meaningless. the message of the drama is "even if someone is not making any good for you and actually making your life worse, if the person is attractive, it's ok" and nabi's life went downhill when she got to know him.

— story: 3/10; bad storyline that leads nowhere, really repetitive.

— acting: 7/10; it's good but didn't stood out that much.

— music: 3/10; really plain.

— rewatch value: 3/10; thanks to soljiwan moments.