I'm not the biggest fan of being told one story only to discover I'm actually being told another. There are times when it helps to be deceived, and then there are times when such deception is little more than a sly paving-over of not having much to say in the first place. HAL uses this kind of storytelling sleight-of-hand, but not in a way that I am prepared to call dishonest; the end result is sincere and even moving. But all the same, would it be gauche to suggest the story we do get is a partly missed opportunity?
Domo arigato, Mr. Roboto
HAL opens with a disaster seen from a distance, from which we are led to believe (you will see soon why I say this) that a young man — the Hal ("Haru") of the title — has died suddenly. His girlfriend, Kurumi, with whom he was preparing to have a life, has collapsed emotionally, and withdrawn to the interior of a closet in her house, where she plays back audiovisual clips from their brief life together. To counter her self-imposed isolation, a plan is devised to take a robot, doll it up to resemble Hal, and send it to her as a companion.
The robot Hal is understandably confused about all this. He's polite, intelligent, and patient, but that doesn't stop Kurumi from slamming doors in his face and ignoring him pointedly. But his persistence pays off, especially after he discovers a set of Rubik's Cubes on which each of them — that is, Kurumi and the original Hal — wrote a number of wishes to be fulfilled. He's able to fulfill one of them for her (it involves buying a fake giraffe), and by degrees she comes to treat him as something more than just an appliance with a cute face.
One of the consequences of Kurumi coming out of her shell is that robo-Hal — and by proxy the audience — learns that much more about the original Hal. He had suffered a ruinous childhood, and the repercussions from that (they mostly involve money) were putting a sharp rift between Hal and Kurumi right up to his death. Maybe the robot can learn how to emulate the best of the original man while shedding the worst — that is, provided his worst doesn't catch up to him.
At this point it becomes impossible to talk properly about the story without a spoiler, so bail now if you remain curious. Hal and Kurumi are attacked, and in the process the audience is subjected to full-length versions of the flashbacks that detailed (albeit incompletely) Hal and Kurumi's life together. From this we learn that Hal is not in fact dead at all, that it was not he who died on that plane but Kurumi, that he has been in a state of shock ever since, and that Kurumi is in fact the android copy, provided for him as part of a psychodrama-like therapy program to restore him to health.
On how it could have been
How you, the audience, take all this is likely to depend on your tolerance for stories that allow the viewer to mislead themselves or to draw the wrong conclusions based on the evidence offered. I suspect the reason they opted for that device here was to provide a way for us to share Hal's feelings in some sense, to experience his gradual coming to terms with the truth. It's not used to cheat or jerk the audience around — or, rather, it's the kind of cheating or manipulation most audiences aren't likely to reject out of hand.
But all the same, I found myself uncomfortable with this twist. Not because of the twist itself, but because of the way the twist replaces one kind of story for another. I wrote before about how part of my initial problem with Attack on Titan was that it started by giving us Saving Private Ryan, but by degrees replaced that with The Amazing Colossal Man (or Big Man Japan, if you want to get really snide). The possibilities inherent in the first kind of story (one about the cost of survival against dehumanizing odds) just seemed all the more interesting to me than the possibilities raised by the second kind (one about people who can pilot what amount to flesh-mecha). But I did my best to put my annoyance aside and let the show unfold, and that bit of self-discipline helped me to see the show that was actually there, not the show I wanted to see.
In the same way, I spent a good deal of thought on whether or not the creators of HAL -- director Ryōtarō Makihara, producer George Wada (Attack on Titan) -- had cheated themselves out of making a really great film by not ditching the big plot twist and just making something about the fundamental impossibility of replacing those who have been lost. But the more I thought about it, the more I realized the movie was about that issue; it had just chosen to approach it in a way I wouldn't have, had I created it. Pine as I might for the movie I could only see in my head, it didn't exist. Good or bad, the HAL I got did exist, and I had to review that film on its own merits.
I lay all this out as a way of saying that the problems I know I have with the film shouldn't get in the way of most peoples' abilities to enjoy it. HAL does far more things right than wrong, not least of which being it doesn't wear out its welcome: it's only an hour long, and so doesn't become flabby or digressive. The only way to make it work as a long project would have been, I guess, to embed the above revelation inside a much larger story — e.g., perhaps this was all being done against both of their wills, and they have to escape from the confines of psychodrama a la the climax in Satoshi Kon's Perfect Blue -- but, again, that's not the story they were aiming for. I'll leave it to you to decide for yourself whether they should have aimed for such things after all, or if what we have is already everything it needs to be.