For the record, I haven't been able to clear Kurogane either, including with Gronia. But regardless, congrats on the pulls, especially the Gronia! My Gronia team's so tanky it's unbelievable; with Nees on the team I pass 100k HP! I do sometimes wish its damage was higher, but packing a burst inherit and making 7+ combos does help a lot (especially if you are able to fit an L-block for Gronia in there somewhere). And Ragnarok Dragon with a God Killer SA and God Killer latents blows through God-type enemies like a blowtorch through tissue paper.