It could be to give the girl a more distinctive look. Sometimes, covering an eye with hair can make the character seem more intriguing or have a certain charm. Also, it might be part of the creator's artistic choice to convey a particular mood or personality trait.
Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
The key to a great comic cover design is to think about what would make someone stop and look. It could be a unique art style, a powerful image, or a combination of colors that stands out. Maybe incorporate a bit of mystery or a teaser to make people want to pick up the comic and find out more.
First, consider the genre and target audience of your comic. Then, focus on creating a visually striking composition. Maybe incorporate elements that hint at the plot or main characters. Good typography can also add to the appeal.
As of now, Sanji is very much alive in the One Piece manga. The story keeps unfolding with him as a vital part of the plot. The author hasn't written his death yet.