[Very. Incredibly sad. The feelings she's experiencing are much worse than being forgotten, worse than fading away. Fuuko really loves it here in the village, it gave her a chance to meet new people and make friends. Being here allowed her to do what she told her sister she was going to do on the day of the entrance ceremony. She can't say she hates it here, even with the experiments. There's more of a life for her here then there is back home...

And yet, Nagisa. Why now, of all times she disappears now.]

... Yes, Fuuko is sad. If Fuuko wasn't sad right now then Fuuko and Nagisa-san could not have been very good friends.