Contrived horribly contrived.
Imagine extending O'Henry's gift of the Magi to 5 hours long with episodes and adding in pointless extraneous characters, then trying to mix things up a little so it's not painfully obvious you are lifting other people's work.
If that doesn't work for you another way to think of this is as a romcom, that has all kinds of romcom gags but with no humor whatsoever. It has all the stupid things you expect from a romcom, the people who are hopelessly unable to get out of their way, annoying foil characters, ridiculous situations, complete lack of communications between the main characters, the supporting characters, and even reality. Just no laughter at all.
If the above doesn't paint a picture for you, try think of My Teenage Romantic Comedy SNAFU, but with more characters who are more self destructive than Hachiman. A main character who you would think could only have a love life with a necromancer. Toss in a couple of love triangles that have no reason to exist. Take the pacing down to Methuselah going uphill in winter. Discard all the self examination of SNAFU. Then you may have a pretty good idea of what Just Because is like.
If you have heard the phrase, "more than the sum of its parts', here's your chance to get acquainted with the opposite, "Less than the sum of it's parts". Just Because has well developed characters, the problem is they don't make you care about them at all. The acting, the tempo of their lives, and the portrayal by the voice actors leaves you wondering why anyone would expect you to care about these people. You don't care about the hopeless loser characters. You don't care about friendly characters. You don't care about the main characters. You start with that fail then you add in what should have been at most a 3 episode story stretched to 12 and the next thing you know you have characters + story < (character) or (story). That black hole of a combination then sucks in to its depths what was some very good art and pretty good music.
Matter of fact, there were some of the best background art you could hope to see in anime here. I particular enjoyed the town where it was set. The problem it was attached to the characters and story which killed the great art and the good sound.
All I can say, is you can put this on, leave it on, never have to worry about paying attention to it, never have to worry about being surprised, and be absolutely certain it won't directly perturb your emotional state at all. It might make you angry with yourself though, for wasting time watching it.