Normally I don't even watch trailers because they ruin too much of the film by showing all the best parts or too many scenes from the third act. But the trailer is essential because you'll immediately know if this film is up your alley or not.
 

I didn't research it at all until after the film was over. But I recognized the art style from "Space Dandy" and "Ping Pong" and "DevilMan: Crybaby." The dude is iconic and you'll see nothing like it anywhere else. Great mental palate cleanser if you feel like you're in an entertainment/art rut.
 

However, this is one of his most bizarre works if not the most bizarre. (I have yet to watch his full filmography and don't know much about him.) So you'll only enjoy it if you are an artsy type or you smoke weed before watching. The plot and symbolism is very hard to decipher and I'm not sure what to make of it all. Tried googling because even just the basic surface level plot went over my head – especially at the end – but couldn't find any breakdowns.
 

Was the yakuza guy in the beginning the old man in the Whale? Whose lives were they following? I guess the "this story has never ended" thing was talking about these dynamics of unrequited love, life path regrets, & wishing you could turn back time, that reoccur throughout all humanity? And it wasn't trying to literally say they were the same people but just showing all of the different possible life paths and common themes connected between the characters? I don't know, man...
 

In my futile search for any sort of analysis, I found this blog and she has the best guidance for viewers:
  

I advise you now to not focus too much on deciphering things, but rather just sit back, relax, and wallow in the dazzling animation.

 
I think people like Yuasa perform best when grounded by some structure on the production team. This could have been a more coherent psychedelic classic like "Paprika" if it had a few boundaries. But consider this like his improv jazz B Side or something and just enjoy the visuals & experimentation.