Nice image but what has been seen...

Sakuya (proportions are so messed up if you think about it looking under Remi's chin)

On the plus side tho

Flandre + boobs = Win/win

I see what you're saying, but Sakuya could be wearing her apron tied very high (right under her pads). We can't see her hips, so it could go either way.

Why she'd wear it like that is a different question...

The apron is out past her shoulder almost and it should gather at her waist I would think.

I don't get what you mean with the shoulders. I also think it could be that apron is worn very high above her waistline.

Draw a line straight down from Sakuya right shoulder (or left but right is more visible) past flan's hair. The chest (not breasts) is basically wider then her shoulders, as is her waist with no curve (she should be hourglass) at the bottom of her rib cage at all.

The apron should wrap around at the width of her bust at the maximum (likely less since her bust in the image extend out past the width of her rib cage). As the image is atm, she defies human anatomy.

Also we will not get into how messed up he legs are (think width and curvature vs her height). See should be at best as tall as Remi.

She is just wearing body armor under her clothes because Flandre is around.

Behold Pure Elegance