This is it, right?

With the skirt removed, the feeling of her being tied up is more pronounced. The artist here uses 'NUG', likely an abbreviation for 'nugu' (脱ぐ), meaning 'to take off'.

Ugh...

The way the crotch rope digs into her is pretty painful.

If she doesn't lift up her skirt, she looks like just another ordinary schoolgirl.

Restraints that cannot be seen if it is not shown.

This is indeed quite sensitive...

Um,

Please don't look at me, mister.

It's embarrassing...

When the sailor collar and shirt are fully opened, the bound body is exposed.

I am thrilled by the fact that if it none of this was already visible, no one would know it was even there.