Why are her bloomers down?

because she's jumping?

also, those jiggles

Koucchan said:

Why are her bloomers down?

Newton's Third Law of Motion: Every action has an equal and opposite reaction. When the breast bounces upwards, this produces an reaction force that is acting on the opposite direction, pushing the bloomers downwards.
(Totally bullshitting)

laisy said:

Newton's Third Law of Motion: Every action has an equal and opposite reaction. When the breast bounces upwards, this produces an reaction force that is acting on the opposite direction, pushing the bloomers downwards.
(Totally bullshitting)

That or they began slipping from her jumping and her tied arms disable her ability to remedy the situation.

Akagi-senpai is training her.