If you loved One Piece: Giant Mecha Soldier of Karakuri Castle, try One Piece: Episode of Skypiea
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

One Piece: Giant Mecha Soldier of Karakuri Castle
→
Try this next

One Piece: Episode of Skypiea
What they share
Both films are directed by Konosuke Uda, and they both carry the playful, uplifting mood tags, and they sit in Action / Adventure / Animation / Comedy territory. If that's the register that drew you to One Piece: Giant Mecha Soldier of Karakuri Castle, the second film will land in a comparable space — through a different lens.
playfuluplifting
What One Piece: Episode of Skypiea is
Some islands just refuse to stay on the ground. A misplaced cloud-surfing tribe and a self-appointed deity make life messy for rubber boys on their way to golden real estate. The whole thing folds up neatly the second the credits roll.