Vercure is water, based on its blue animation (compare to veraero's green aura).
My headcanon is that Fleche uses ice aether, despite the flavor text calling it unaspected. It's clearly different than Contre Sixte, where they explode into pillar of blue light. The swords impale and it appears to me to look like it could be ice. It would make sense that by 70, RDM has all 6 elemental aspects represented, and since we didnt get a more clear water or ice skill by 80, it reinforces the notion that Fleche/Vercure are ice/water respectively imo.