It could be because it taps into common teenage emotions and experiences that people can relate to.
I think it's because it offers a fresh perspective on the challenges and vulnerabilities of highschool life. The way the girl's embarrassment is depicted might be very realistic and touching, which attracts a lot of readers.
It could be that the punishment is too harsh for her and makes her embarrassed. Or she might think others will look down on her because of it.
To draw a manga girl in an embarrassed pose, think about her body language. She might hunch her shoulders, tuck in her chin, and have wide eyes. Also, add some sweat drops for effect.
Maybe she's shy or something happened that made her feel awkward.
It could be that in the manga world she's in, having that kind of strength isn't considered 'normal' and she's worried about being judged. Another reason might be that her strength has caused problems or misunderstandings with others.
It could be that she was caught in an unexpected and awkward situation, like tripping and falling in front of a crowd. Or perhaps she was wearing something that she thought was inappropriate for the outdoors.
To draw embarrassed cartoon eyes, first, draw big round eyes. Then, add a hint of red on the cheeks and maybe a few sweat drops. Make the eyebrows raised and curved to show the surprise or nervousness. Also, a slight tremble in the eyelashes can enhance the effect.
The girl in the cartoon might be embarrassed because she was rejected or didn't perform well in a task. Maybe she had a misunderstanding that led to an awkward moment.
Friendship and romance are often big themes. Girls in high school manga usually deal with making friends and having crushes.
The appeal lies in the novelty of the setting. A high school girl in a bartending role brings an unexpected element. It also explores themes of growth, responsibility, and finding one's place. The visuals and character development often draw readers in.