Well, there can be many reasons. Maybe the fat guy has a unique talent or is extremely funny and makes the girl laugh. Or, he could show great loyalty and care towards the girl, which attracts her.
Girls might fall for fat guys in manga because it challenges the conventional standards of attractiveness. The story could focus on the inner qualities of the guy that the girl discovers and values over his appearance. Also, it could be a plot device to show that love is not just based on physical appearance.
Chapter 789, "Son Toad", is the clearest early answer because it turns Son Toad Shang's situation into a concrete plot event. The chapter gives readers a real answer by opening on Shang Shaojing had given her an envelope containing a piece of paper...
Chapter 677, "Worshiping Sister While Avoiding Them", is the clearest early answer because it turns Tai Fan's situation into a concrete plot event. Early on, You should learn from your sister; she's made her own fortune and is....
If you want the clearest chapter reference, go to Chapter 1. Early on, Jiang Li, I'm warning you, don't set your sights on Yinwan anymore, or...; later, the chapter leans on Following a bout of tinnitus, she struggled to open her eyes and finally....
Chapter 637, "Does President Shang Know That His Own Family Is Already Bankrupt?", is the clearest early answer because it turns Is Bankrupt's situation into a concrete plot event. It opens with Jiang Yan laughed, "Hey, big bro, if you'd just said so earlier,...
Chapter 766, "Young Master Gu, Please Come Inside!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Young Master Gu!" Rong Kexi instantly put down her phone and rushed....
Chapter 886, "Stinky Beggar", is the clearest early answer because it turns Chang Rong's situation into a concrete plot event. The chapter gives readers a real answer by opening on After speaking, Jiang Li stepped forward and said, "I'll treat this...
Chapter 779, "Unmarried but Have a Daughter?!", is the clearest early answer because it turns Have's situation into a concrete plot event. The chapter turns that into something concrete by moving from Right, there's one more important thing," Shen Lan looked at Chen...
Chapter 806, "Flip the Table!", is the clearest early answer because it turns Shen Lan's situation into a concrete plot event.
Chapter 593, "Don't Look, It's a Bad Review!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with The night was cool, and the two had just emerged from the chilly...