What's the fastest way to farm Black Shards?
I only have one Black Shard. I've found a boss in Chaos Shrine who drops them, but the song usually ends before I can beat her, even with my good team. The other shards, I've been able to get two at a time easily and fight multiple bosses in one song.
Is there a better way to grind for Black Shards?
SO far, I've only found 2 or 3 bosses with black shards in the Chaos Notes. Bosses 2 and 3 both drop black shards in "No. 78, Mvmt. 55 - Minuet - [Samsara's Revenge]"
So if you know the trick about how to fight both bosses in one go, you can try that one (though I usually only get through one boss, anyway, on that one).
The other black shards I've found are in "No. 59, Mvmt. 13 - Lullaby - [Victory's Perspective]" vs. Bosses No. 1 and No. 3.
Also, a Rainbow shard (if you need them, can be found in "No. 26, Mvmt. 76 - Lament - [The Lands Pathos]" against Boss No. 2.