Wagner's Ride of the... Samurai?
Valhalla Knights, eh? I'm imagining a bunch of archaic-speaking, coat-of-arms bearing history-lecturers in rusty metal escorting the dead to a lofty marble hall of wine & drink in the sky... Interesting transition from a horde of screeching, bloated dykes in breastplates waving around spears - I still have the utmost respect for them, mind you, as with any established operatic musician. But that has nothing to do with the movie.
Haven't seen any substantial bridge between the opening confrontation and the continuning storyline... apart from that hear-jewel thingo. The whole thing's like a Norse mythology anime, but that just makes it even more irregular and out of place.
As you may have guessed, I am a proficient student of mythology - it's a powerful tool - use it wisely. Good luck.