SERO-338 - Mask no Susume - Ichiban Yabai JK Enkou wa Kore! FILE 01

When she's wearing the mask, they focus entirely on her crotch; once it's off, they focus on her eyes, expressions, and face. Her mouth acting is actually quite detailed. The only disappointment is that the final facial shot failed, so her face didn't get covered properly. That was the highlight of the film, so failing there costs it a point.