If you loved Saint Seiya: Legend of Sanctuary, try One Piece "3D2Y": Overcome Ace's Death! Luffy's Vow to his Friends
A bridge between a film you've already seen and one most people haven't. One Piece "3D2Y": Overcome Ace's Death! Luffy's Vow to his Friends has roughly 3.8× fewer votes than Saint Seiya: Legend of Sanctuary — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.

Saint Seiya: Legend of Sanctuary

One Piece "3D2Y": Overcome Ace's Death! Luffy's Vow to his Friends
What they share
Theysit in Action / Animation / Fantasy territory. If that's the register that drew you to Saint Seiya: Legend of Sanctuary, the second film will land in a comparable space — through a different lens.
What One Piece "3D2Y": Overcome Ace's Death! Luffy's Vow to his Friends is
Here's a film that apparently fills in a gap. Luffy trains, but his routine gets disrupted when pirate Byrnndi World kidnaps Hancock's sisters. Luffy and Hancock then team up to save them from the World Government's hostage situation. It probably did well with its target audience.