
I'm not sure why they chose to dispense with so many structural problems like that, either. If they wanted an Isekai where the point of the story was NOT that the main character becomes pretty after developing some emotional protection from her insecurities, develops a reasonable relationship with her family, and acquires the independent source of financial wherewithal and safety to move around that world with autonomy, why did the author transmigrate her into that situation in the first place? If they want all these core issues to be resolved right away so that they can get on with "the story", why create them at all?

did you not read the story at all??
first) She NEVER used magic to lose weight. She was training her mana and she herself didn’t know her body would do that, that’s why MC is surprised.
second) Her personality didn’t improve because she lost weight. ITS BECAUSE SHE IS A DIFFERENT PERSON LIVING IN THE MC’S BODY!!! did u miss that part at the beginning of this?? The new person in MC’s body was confident BEFORE she lost weight too. How she talked back to the duke even when she was fat and her brother and apologizing to her sister?! that happened when she was fat!!!
third) the ppl being hypocrites is trash but every isekai manga/hwa is like that

She was a skinny person in her past life... the MC’s body isn’t the result of eating healthy and gaining good weight but rather her overeating because of stress and depression. She(real MC) overate because she had depression, and then when she saw her "unsightly" body she got more depressed and ate more. The new MC knew her weight was mostly waste(there is a thing like good fat and bad fat look it up) and when she practiced her mana her body shed the wastes from her body which is the bad fat she accumulated from depression and overeating.
ALSO SHE NEVER RESORTED TO LOSING WEIGHT!!! SHE PRACTICED HER MANA AND HER BODY FAT MELTING WAS ONE OF THE BY PRODUCTS. she never did it to lose weight

She did not "immediately resorted to lose weight to solve her issues", she never knew that by cultivating her mana, she would lose weight at a drastic rate. Like a commenter said, losing weight was a byproduct of her trying out the mana, and not an intended result since she never specifically said "I need to lose weight".
If you read again ch 3, you'll see that mc says that Sylvia doesn't look bad at all, she has charms and aura of her own, but the original Sylvia couldn't see that because she had inferiority complex. And again, if you truly truly read chapter 3 properly, you'll understand her train of thoughts. The first thing she thought of to escape from Sylvia's fate was to have power and money, she explicitly said that there's no point in caring about what others think of her, and never- I repeat, NEVER did she ever thought of trying to slim herself down to solve issues. In the first place, it's not her issue nor problem, it's Sylvia's problem. Sylvia was the one who needed to learn that beauty is not only on the outside. It was Sylvia who needed to overcome her insecurity. Not mc. MC is already a confident person, and even before she got slim, she already talked back to the father confidently, and confronted the sister sincerely. Now that is the way to solve Sylvia's issues. Like I said, YOU'RE the one who can't read lolol. You can't even comprehend simple stuff like MC's narration. Not once did she say "losing weight is going to solve this issue".

Even if the author acknowledges that the LC's insecurities and jealousy about her appearance and abilities did not happen in some sort of emotional vacuum where negative reinforcement did not happen frequently and unfairly, the implication that the character's weight was somehow related to her soul quality instead of her basic physical metabolism is deeply offensive, just as the idea that an increased breath mana technique which causes fat to literally drip off the body isn't magical fairy fart hocus-pocus is LOLOLOLOLOL. It's too Cinderella's fairy godmother for me. I almost expected the bathtub to start singing "bibbety-bobbity-boo", ya know, between acid reflux burps.
But the most offensive idea of all is that, as a chubby girl, she was not considered perfectly beautiful and worthy of love and nurtured just for who she was. The author did a lot of women a grave disservice there. Too bad that point hasn't been acknowledged.
So, what do we get to look forward to next? Black face?

Her cultivating mana get rids of any "waste" to the body. And her fat is a waste. there is good fat and bad fat, good fat being you eat healthy and do adequate amounts of exercise to build muscles. HOWEVER her fat came from her inferiority complex which led to her being stressed/depressed which led to her overeating. That is a VERY unhealthy way to gain mass. Plenty of obese ppl do surgery to get rid of extra mass on their bodies that aren’t good for them. i wouldn’t say MC is obese but she’s not very healthy either.
for your second paragraph many ppl see to have this misunderstanding; the original MC was not hated for her body shape, in fact as a child she was skinny. Ppl compared her to her "perfect" sister and bullied her on that. NOT HER BODY SHAPE. and when she gained the inferiority complex towards her sister, she bullied the blond sister which in turn made things worse for her and she was bullied more. DURING ALL THIS the MC was not overweight. So your point there is also invalid. Yes she later overate and became overweight but she wasn’t loved even before that so....
Y’all are trying so hard to prove it’s fatphobic that most of y’all are actually skipping over important facts given in the manhwa itself. The MC never once related overweight to being ugly. she just said she didn’t take care of her appearance; face, hair and body. and let’s be honest. she didn’t.

No, we aren't trying to "prove" anything. That would imply that we have something at stake in this manhua, other than the desire to read a good story, one which isn't intrinsically offensive and doesn't make a marginalized group of people feel like shit for reading it. Don't give AFF for the justification crap.

Not everybody agrees with your "key points in the manhwa" for one thing. I saw sloppy, threadbare, lazy-assed story structure and character development that only made sense in terms of "let's roll over this with as quickly as possible, even if it insults our readers", and the OP saw and felt body-shaming marginalization and said so. Then, a whole bunch jumped all over her in their haste to invalidate her feelings and squawk at how dare she have a different opinion. So ... yeah. I'm just here to tell her I can see her perspective and support her to feel what she feels, and if people don't like that, tough.

nobody is talking about the flow or structure of the story. i’m saying y’all IGNORING actual pointers given in the manhwa to draw your own fatphobic conclusions. None of what you and the original commenter said happened in the manhwa. She was bullied before she was overweight not after. her being fat is not the main cause of the bullying. Her soul quality being related to her body??? that never happened too. The original MC has felt like she didn’t belong since way before she was overweight so y’all making it seem like the author is fatphobic and saying everything bad is happening coz she’s fat when that’s not true. Also why should the new MC have to deal with the original MC’s fcked up overeating and body? Even if she DID use magic to get rid of the waste she’d be in complete right.

Because the argument is ridiculous from the start. Everything that op said can be refuted back if op only read the story properly.
The first point of Sylvia losing weight without any effort is not even a valid argument. If the story is about Sylvia getting reborn, then showing the process and her effort of trying to take care of herself better would be a development in her character, hence there would be an importance in showing effort to slim down and have a healthier body. However, the story is about a transmigrated mc, who actually has no problem of insecurity or inferiority complex, and is already very confident, and she also explicitly said that Sylvia doesnt look that bad and has an aura and charm of her own. Therefore slimming down or showing the process and effort in being healthier is pointless because there would not be any effect on mc's attitude nor character. Because in the first place, the problem of having an unhealthy body is original Sylvia's problem,

* it's the original Sylvia's problem, not the transmigrated mc's problem. And op's point of her personality became better after she's skinny is also ridiculous, because the soul in Sylvia's body is a different person entirely. Even when mc was in sylvia's overweight body, she was already confident and had never made a plan to slim down. She did not "gain confidence by losing weight using magic" like op claimed, MC WAS ALREADY A CONFIDENT PERSON. The "hypocrites" did not treat her better because she was skinny, even before she got fat, she was already mistreated. And the servants' gossip that she has changed mostly revolved around how she complimented the chef, or give chapsticks, give them medicines, and even greeted them, these are all the type of stuff that original Sylvia never did, so of course they would be surprised and delighted by her change because it is true that on the surface, Sylvia has changed for the better in their opinion. Her father and brother are trash and there's no denying that, however just because their personalities are trash, does not make this story garbage. Op also said that Sylvia immediately resorted to losing weight to solve her problems WHICH ARE NOT TRUE BECAUSE SHE NEVER EVEN MENTIONED THAT SHE WANTED TO LOSE WEIGHT, IT'S A FKING BYPRODUCT OF HER TRYING OUT HER MANA BECAUSE THE FIRST THING SHE WANTS TO ACHIEVE IS POWER, NOT FUCKING BEAUTY. So yeah, in conclusion, op IS too stupid to comprehend the story. And it seems like you're also too stupid since you believed op's words to be justified. Congratulations on not winning an argument you yourself are too dumb to realize that the points made did not make sense at all.

YES it flew by me and straight into the dumpster because you and OP made literally 0 points with what is happening in the manhwa. I’m making sure i understand the story and you are giving reasons to hate that DO NOT EXIST!! Your level of comprehension isn’t even comprehension because to comprehend means to understand and you literally understood nothing of what is happening so congratulations on being dumb enough to not even READ WHAT IS INFRONT OF YOUR EYES! How can i win this argument when the people who started this argument make up false reasons to hate it? There was no argument from the start. an argument would be us disagreeing on the same subject. You and OP however went completely off the rails and wrote your own versions of the story, talking about shit that never happened. i will take this win gracefully and since you and OP seem to hate this story so much that it seems you would drop it! yay for me! less people to educate ppl who continue to be dumb till the end :) i will be muting this so if u do reply u will be talking to urself
Just my opinion, But the story is just getting worst. It’s total garbage. Sylvia loss weight without any effort at all. And OMG her personality becomes better after shes become skinny like WTF. You would think that her personality got better cuz of how everyone going to treat her better cuz she’s beautiful now but NO. She gained confidence by losing weight by magic!!!! And all those hypocrites treating her better cuz she’s skinny now.
The whole story is about lying appearances not personality at all. Cuz if we are talking about personalities then all the characters including mc are trash. The father and brothers preferring their angelic sister are trash. The angelic sister stealing the lights from her sister not thinking about her feelings is a trash.