When talking about the story of the manga, we can separate the story in two aspects:the more sci-fi aspect, and the more romance one. I will separate them because in the sci-fi aspect the story fail horribly and in the romance aspect it succeed quite well. So let's dive in.
In the sci-fi parts we have an UFO that appear just above Tokyo, and just as it appears the main character meets with his ex-girlfriend and reunites with her. After that we suddenly discover there are several versions of his ex and the one he met was actually is an alien. From there the plot get more complex (unnecessarily) as there are people that want to use her for their own good. The story fail hard early on because of unrealistic situations and reactions from people. Now I know what you will say "It's a sci-fi story, so it's okay for it to be unrealistic, right?"
While that might be true there are a lot of things that still need to remain realistic. For example the reactions of the people to the alien are very nonchalant, the "villain" of the story is a crazy soldier that you wonder why he is still a captain in the SDF. I mean, he shoots anti-tank missile on small target in the middle of Tokyo and no one in the government or the army gives a shit, apparently.
That's just the tip of the iceberg as there are sudden, random betrayal, plan to rule the world that is simply forgotten by everyone in the end, details that the bad guy knows just because and of course a skip in time that make us wonder "what the hell happened?" yeah, the story is just isn't that good.
Now for the romantic aspect, it is way better. The story begins with a love that already ended, and although the romance itself isn't the best thing ever, the themes behind it are great. Staying true to your emotions, not denying them, understanding how important something was to you. If the sci-fi part wasn't so serious, the manga would had been much better.
As for the characters, we have the main character which is a pretty bland guy. The main thing that affect him is Ashita, his ex. We have three versions of her in the story, two younger versions and one that is older. By being with her he can understand how much he loves her and how special their relationship. As for the minor characters, they are all carbon box that exist only to say how cute Ashita and some of them to advance the sci-fi plot.
The art is not bad, but not good either. It's pretty average. The only thing that I really loved about the art is the character design of Ashita herself. The artist gave her some nice lips. But that's about it.
All in all, that's a short manga that I think you should read if you care more about the romance and true love. Although the conclusion is pretty obvious it still nice to see how the manga present the regret and the passion to return to a love that lost.
