Please Teacher!

One night while Kei Kusanagi is resting by a lake he sees a UFO crash into it. He jumps to his feet and suddenly sees a glowing woman appear on the lake. He runs away screaming but his world abruptly goes blank and he enters a "standstill". The next day at school, the class has a new teacher named Mizuho Kazami who turns out to be the strange woman from the previous night! Was it all a dream? And what will happen when Mizuho is Kei's new neighbor?