Meh. The main plot of this story starts with technology from a race so advanced that they see time travel as trivial being destroyed by liquid. I say in reviews often that having a perfect story is bare minimum. Aside from that it's an okay manga. It's sad? The ending will make your heart go fuwafuwa. It's similar to "In the Gardens of Gehenna" where the plot essentially revolves around children from broken homes trying to coexist and failing to. Aside from that, the chemistry between the characters is just okay, I guess? Tragic manga try more to pull on your heart strings and make you feel bad for the characters than anything else. The art lends itself to that purpose and it does a great job at it. Once you get past that core gimick, everything else, from the logic underpining the story, to the characters, to the worldbuilding, to the chemistry between the characters, etc, is just mediocre. Kuze, Marina, and Azuma essentially have the same personality but with different circumstances. It's something manga in this genre in general struggle very hard to do.
If you want to feel sad, this manga is for you, otherwise it's just bad. 3/10.
The only reason I'm not rating it lower is because the art lends itself to the narrative really well. The art in "The summer Hikaru died" is much better and a similar style but this manga's art is nothing to scoff at.