Well, I really wanted to say this about this drama.
You have to watch it! Why? Well, because the story will drive you crazy when he returns in time over and over again and you will actualy get to tell the characters what they should do.
I really liked it until episode 9 inclusive, but the final episode it shouldn't have existed or maybe just the first minutes of it and an explanation about what happened with the other characters.
And now something about the characters:

Harumi was such a great character because he seemed to have anticipated the future.
Dojima Otaro (Eight) is a character which evolves throughout the story, but I really did not like how he returned in time in the last episode and for the last time because it was unfair for Saiko, the present one.
Saiko seemed to me a little bit naive, but she helped Eight to evolve and she give him a new perspective about his life.
Takauji Namiki was interesting and, I think, the creators should have given him some extra moments with Saiko.

What I did not like:
- the final episode (because Saiko did what she did with a purpose and I really liked that present, not another one)
- I think that Shison Jun (the actor who played Osanai Kazuma) did not illustrated his character as it should have been.

Overall, it was an addicting drama and I will surely rewatch it.

Oh, and Sayonara Elegy (the melody from this show) is really a melody which helps shape the story.