Hm, I played through the demo just yesterday. To begin, I congratulate you for finishing a demo! Until now, none of my three projects has a demo, so just reaching to that point is a small success :3
I rather like the mood of the game, the demo itself showed a quite professional feel. The story itself flowed quite nice, but there's a question in my head that's going on:
Well, what really happened to Nagisa that made him fear water? I feel that the prologue didn't really elaborate much, except if it's really just supposed to be a teaser and the whole thing will be revealed mid-game.
Then, the part where the flood comes in. I was going after Atsuhi, well
I saved him from "drowning" when he fell in head-first in the water
and plus, at the part where the map menu comes in, I didn't really know where to go and I ended up going in the wrong places XD I only realized I should go in the third years when Atsuhi said something like "What are we doing here?" XD
And back into the flood part well, I don't think that they'd like to keep the students in after a flood, right? When a storm comes in, the students or the faculty would like to have at least a contact on the outside world, like a TV in the faculty. In here, one of the students have a phone that has a TV in it that'll keep us updated everytime a strong rain comes, in case The DepEd would like to suspend classes. If the reception was cut as soon as the storm hit, you can ignore everything I said. XD But seriously, you could have at least tried suspending classes in there, but Nagisa and Atsuhi and the rest can't make it out because of the rising water level.
The music was also nice, I like how in some parts you didn't put music but instead only an "ambiance" tone in it. I actually didn't notice there was music until
the lights flickered in the classroom or something. XD
The only in-game thing that bugged me was Nagisa's narration. It would have stood out better if you remove the Nagisa tag and the parenthesis when he's narrating. And also the pauses... I first thought that the pause were the won't-continue-until-you-click type, until I accidentally missed some text because I keep on clicking. XD
Overall, good job! I'm looking forward to your release~