I love the colours, style and shape!
However, as always my critique will function of the “usefulness” of the sword – as far as I see it, one of the important things about Stonehearth’s style is that everything in it is believable and looks like it would work (even if it’s obviously powered by magic), and if you can match that was well as having really cool colours and shapes and so on then your designs will have that extra level of immersion.
So, the first thing I think about a sword like this is that it’s clearly built for swinging around in big arcs, slicing right through the target; so the double-edged blade is perfect for that. However, I feel like the flared-out end should either also have a sharp edge, or else it should clearly not just be an extension of the blade but some kind of weighted (and therefore thicker) counter-pommel balance… thing.
And again, the question of whether this is a flat blade with filleted edges or an angled blade with a central spine is nagging at the edge of my mind. The tang component that comes down from the cross-guard along the blade itself would suggest an angled blade; but your edges are currently highlighted as though the blade is flat…
Some really great advice I got from painting Warhammer models is to never make your blacks “just” black. It has nothing to do with the myth of “there’s no true black in nature”; rather it’s because the eye can’t really pick out shapes so well when the shape is just an area of black. I’d suggest you add some really dark charcoal grey “fading” around the edges, with pure black in the middle of the blade.
Thinking back to your older blades, that “broadsword” style with a central raised spine would, I think, work really well here. You could even make this blade a little wider, and then have your very thin and very bright highlight for the central spine, with similarly bright edges and an abrupt fade from that bright silver to dark grey and then a very dark charcoal. The same patterning could be used to imply that the end of the blade is thicker/meatier, so that the end looks a bit more dangerous and less blunt.
Reference image: Sword of Silence | Warhammer 40k | FANDOM powered by Wikia
It’s obviously not quite the same shape, but that image shows how the blade could be angled along its length and then flare out at the end.