
I am sorry to inform that it is not true. For example, I had a childhood friend, since high school, she was a cup E or F, and she was very slim. So, I don't know what you are talking about. Boobs are always fats. So, people can be naturally slim and have big boobs. You are acting you never walked in the streets or beach and saw slim girls with big boobs. I don't know who lied to you about about how boobs fat works, but google a bit before.

Well, if you're happened to be a man. Most people are just blessed with boobahs despite their thin frame but that's literally suffering. Coco melons weights similar to actual ones, that's why most girls hunches their backs lol.
And it's a common knowledge that if you have boob fats, there should be back arm fats. That goes the same if you have thicc thighs, soft or pudgy stomachs should be given.

Rather than common knowledge, it's my first time ever reading this misconception of yours, and I was very attentive in biology and biochemistry.
Every boobs are fats, not all huge booba owners have fatty arms. Just google, gain some REAL knowledge. And I just clearly told you with my friend. And boobs fats and arms' fat do not operate the same. For example, you can lose arms fat with exercise, but not lose boobs fats with the same method. The size of the bra might change, but rarely does the cup. Additionally, breast tissue is made up of both fatty tissue and glandular tissue, and the ratio between these two types of tissue can vary. This is another reason why someone might have large breasts but relatively lean arms or other body parts.
Some people have naturally nice hourglass shape, either it is genetics or shape-exercices. Got a friend who was complexed about looking like A4 paper shape, so she did exercise everyday to get a hourglass figure, specially working out to get a bubbly buts and shaping her waist. She is still thin, and her stomach is average; she got the hourglass she wanted. Now on the genetics, my E-F cup was well shaped. I mean some people are just born blessed with genetics.
Just because of you have back pains over just a B cup is something that concerns you. You might as well reconsider the bras you are wearing. Rarely hear people with less than a D-cup complaining about this anyway. I will say the coco melons comparison is a wild exaggeration. Very wild, the average weight of one boob is about 0.9lb, and a melon, about 2-8 lbs. Melons are heavy and big too; plus water is heavier than fat.
Ultimately, everyone’s experience with breast size is different, and not everyone with large breasts will face issues like back pain. And I cannot talk for my said childhood friend, since I don't inquire her about such indiscreet question - pretty rude. So, I clearly said I did not know. I don't know, I am not hers. Maybe she does, maybe she does not. Now that I am talking of her, I have an older friend with pretty much the same shape of her too. Can't say for the back pain - that's very rude to ask.
I am more inclined to believe that you might be on the chubby side. I might be very wrong and I apologize in advance for this rudeness of mine. But I simply find your pseudo knowledge totally farfetched, since it is untrue. Based on your idea of "common knowledge", so you might have commonly encountered chubby bodies. You can be a bit chubby and perfectly fit a Small, but there are people who regularly exercise or are just blessed with metabolism with little fats in the areas you highlight depending of the morphology.

I'm not on the chubby side bro. I don't even know anymore what you're pointing at. I was pointing the manhwa female leads first and you decided to made your friend as as example. I said I haven't seen right? And you did but I didn't say that I invalidated her. I just said that it's commonly for people that once they had fats on their tatas, other body fats existed.
I never said they are unrealistic, I just said I didn't see one and I do encountered some but those people openly revealed they had it through gym or surgery.
no, I am really a hater. Fl arms on manhwas are so thin that Ml could like break it like s crusty twig lawl. It's so weird. Some of them looking like teenagers with huge boobs and stuff. ╥﹏╥