Maybe she's part of a crucial plot or character development. It could be to add depth or create a certain mood.
The tired girl might be there to show the effects of a particular situation or to contrast with other energetic characters. It could also be a way to introduce a new storyline or theme.
Maybe she's had a long day or didn't get enough sleep. Could be stressed from something going on in her life.
It could be that she's been working hard on something and hasn't had enough rest. Stress or a long day of activities might have taken a toll on her.
It could be that the character is dealing with some emotional turmoil or has been working hard, which is shown through her tired eyes. It might also be a way for the artist to convey a certain mood or atmosphere.
It could be that the artist wanted to convey a certain emotion or state of mind. Or perhaps she's been up for a long time dealing with various challenges in the manga's plot.
Maybe she's had a long, busy day and needs some rest. Or perhaps she's been dealing with a lot of stress.
It could be that she's dealing with a lot of stress in her life, both personal and related to her manga work. That kind of pressure can really take a toll and make her look exhausted.
It could be that she's dealing with a lot of stress in her personal life or has been overexerting herself at school or work. Sometimes, emotional exhaustion can show on a person's face, even in a manga.
It could be to show the character's emotional or physical exhaustion, adding depth to their story.
Maybe it's to show the effects of overexposure to the sun or to convey a sense of exhaustion. Could be part of a story or a visual metaphor.
The way a manga girl is drawn can make her look smug. Maybe she has a smirk on her face and a relaxed posture. Or it could be that she's constantly bragging about her skills or accomplishments, which makes her come across as smug.