Yes a dark heart creates a void…
But there’s actually a pretty deep story that goes further:
An ancient prophetic book (e.g. Dark Prognosticus) leads a misguided member (Count Bleck / Hyness) of a religion (Tribe of Darkness / Jambastion) to release a dark heart (Chaos / Jamba) to create a Void from his fortress (Castle Bleck’s Inner Sanctum / Jambandra’s Divine Terminus ) to destroy the world. The dark heart is ultimately contained by good hearts (Pure Hearts / Spears).
I just beat the game and I was like WTF is all this, but I guess I’ve never really looked into Kirby lore before.