If you loved River, try Beyond the Infinite Two Minutes
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
What they share
Both films are directed by Junta Yamaguchi, and they both carry the mindfuck, playful mood tags, and they sit in Comedy / Science Fiction territory. If that's the register that drew you to River, the second film will land in a comparable space — through a different lens.
mindfuckplayful
What Beyond the Infinite Two Minutes is
Apparently time travel is just a TV broadcast away. A cafe owner discovers his TV shows future events. It predictably complicates his life.

