...so I'm already done farming Volk for the tree.
Kinda overdid it, actually. Probably could have done maybe 8-ish less fights in the past couple days? I accounted for this week's weeklies, but I didn't realize the build times were so long that I"m not going to be done it before next Monday anyway. So I'm pretty sure I'd still have little to no downtime on building even if I'd waited for those weeklies to help. Whoops.
But it was enjoyable, and I was sick, so... fine enough, got a bit of a headstart on a 6*, idk. Back to eHBH for now...
Oh ok, I saw people mention Void Nidhogg, so I assumed there was some sort of drop I had to farm for. My bad.
It just drops the new level of orbs for dark (that you'd otherwise get from some Very Hard story chapters), and you need a lot of those for Spiral (in the character's element) depending on their initial rarity.
High dragon-wise, you need a relatively low number of spheres for some of the last few Spiral nodes (I think it's 8 for 4*, 5 for 5*? looks like only for 4* as well). So that's only 2-4 Standard runs at worst depending on rarity, with Expert being faster. And then the final node of a 5* character's Spiral requires a single tail from Expert. This is for the dragon you'd be fighting (HMS for fire and HJP for dark), though, so you can at least theoretically use that character to get it rather than have to go through a cycle.