ALWAYS smiling. + The front teeth that shows when she smiles is cute.

A cute face and not-so-cute gun.

This is a real minigun's mechanism. Rotates clockwise.

The barrel rotates anti-clockwise.

(Presumed) The mechanism looks something like this

(Link) Used casings are discarded

In Blue Archive, used casings are only shown in special moments (EX. Skills). Is it for a weapon "performance" (for show), or to show resource (realism)?

She has the physicals to lift a heavy machine gun and smile at the same time.

Hidden muscles... Hidden thighs

Yep yep

Her reload animation is her doing maintenance on the gun's frame.

Casings ejected

Rotor (De-linker)

Loads bullet Fires

A weapon design with opposite barrel rotation.

Clip

Clip separated

Feeding round

Round ejection