First thing that comes to my mind: Perverted.
Second thing that comes to my mind: It's just so wrong.
Let me explain the second part as the first one is self explanatory.
The story is about a boy who had a relationship with his teacher. She was just a new teacher in that school to begin with, so how she could accept a boy/student after a few days just sends warning signals to my brain.
This anime really did send a lot of signals. Maybe they thought this is a good storyline that no one has done so far. But since it is regarded as immoral for teachers to date student (high school students), they bumped reality a little to make this possible. How? She's an alien! Yep. That way she isn't restricted to the moral norms of Earthlings. What? That isn't enough? Well, he was there when she arrived. He knows the secret. So, to keep him quiet... No, she didn't kill him. She did try to make advances on him, all to no avail (because she is an alien, who would want to do it with an alien even how voluptuous she is?) Well they were caught all by themselves and that led to a string of events that they have to cover up with the excuse of dating - later on, married. (Since school policy doesn't allow dating relationship between teacher and students and she would be fired, they have to say they've been married before she arrived.) Yes, they did get married. Around the third episode? So fast.
But the boy is still a child! Nope. Apparently he has this disease he calls "standstills" where he would eject himself from reality when he gets too sad. He'll be in a near-coma state. His body stops growing as well. So, even when he looks 15, he was actually 18. Ta-da! Problem solved!
Speaking about this "standstills", even though they said it's rare, I do believe that is what usually happens to depressed people. They eject themselves by sleeping all the time. They escape reality that way.
Going back on topic, the ending was a bit confusing. If what happened was a time travelling effect where you wonder (like the chicken and egg question) if the previous events took place before or after. If they affected the future, or if they were the effect of the past. Or if it wasn't actually all that and the events just repeated themselves somehow?
I guess that's just it. They wanted a teacher-student relationship, they couldn't do it, they knitted a bunch of craziness to make it happen. :)
Is this on my recommendation list? No. But it's not on my Don't Watch This List either. It's bearable. You can watch it if you want to.