I don't see what's so impossible about her bikini?

Alkaeus said:

I don't see what's so impossible about her bikini?

Without the over-the-shoulder part, those 'kinis will slip down once she made any big movement.
To put it in more detail, that kind of bikini only works on medium to small-chested woman because the compress effect provides enough grip to keep the bikini on by putting tension on the upper side. On woman with bigger sized breasts, that compression effect has little to no effect since the breast's malleable enough to distribute the tension away. You can improve this by using bigger cup to achieve same effect, or adding something like elastic band on the upper portion to keep it in place. This design however, does nothing like that, thus doomed to create wardrobe malfunction.

Alkaeus said:

I don't see what's so impossible about her bikini?

Actually, I added that tag because of how it perfectly conforms to her nipples.

Rathurue said:

Without the over-the-shoulder part, those 'kinis will slip down once she made any big movement.
To put it in more detail, that kind of bikini only works on medium to small-chested woman because the compress effect provides enough grip to keep the bikini on by putting tension on the upper side. On woman with bigger sized breasts, that compression effect has little to no effect since the breast's malleable enough to distribute the tension away. You can improve this by using bigger cup to achieve same effect, or adding something like elastic band on the upper portion to keep it in place. This design however, does nothing like that, thus doomed to create wardrobe malfunction.

Grandblue is a game where people wear backless Plate armor. questioning clothing physics isn grade school.