I saw a GIF of this sword set from Monster Hunter on Reddit yesterday and was blown away by the lighting effect. What makes it notable is that the internal illumination shines through a painted surface, something I've never seen done effectively in any kind of prop.
After some Googling I found the build video for the swords from Kamui Cosplay. On the bright side, no pun intended, it includes a very detailed look at how the effect was achieved using LED light strips and translucent EVA foam. That said, there's a whole lot of cheese to slog through to get there. I have nothing but the highest respect for KC's incredible craftsmanship, but the forced cuteness of the opening minutes is a bit much.