If you loved 20th Century Boys 3: Redemption, try 20th Century Boys: Beginning of the End
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.
You already loved

20th Century Boys 3: Redemption
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20th Century Boys: Beginning of the End
What they share
Both films are directed by Yukihiko Tsutsumi, and they sit in Adventure / Mystery / Science Fiction territory. If that's the register that drew you to 20th Century Boys 3: Redemption, the second film will land in a comparable space — through a different lens.
What 20th Century Boys: Beginning of the End is
Summer 1969, a secret base, a rusty bike bell. Kenji and friends battle villains in their imaginations, recording them in a book. Director Yukihiko Tsutsumi brings 90s Japan to life.