The "Harry Potter" comment on the case is a dishonest attempt to lure in Potter fans. Nothing like "Harry Potter", and the "Giants" in the title is more misleading bait.
It sets up an expectation that it utterly fails to deliver on. Disliked it a lot, but saw some potential, and if it hadn't tricked me into thinking it was something it wasn't my rating might have been higher.
I agree with the other comparisons to "A Monster Calls", which I did not like either.