To elaborate more on '1/3 of the quests being clear this with only X element', each floor has 3 quests. 1 of those will 3 will be 'clear it' (once for floors 1-14, twice for floor 15). Another 1 of those will specify the element. The remaining quest for each floor will be either 'at least X number of kamihime survive' or 'use at least X number of Y type of kamihime'. Type being offense/defense/tricky/etc.

What I'm not clear on is, do reserves count for the 'use X of Y type' quest? Like if the quest asks for 2 offense types, can you leave two in the sub slots and be ok? Or do they need to be in the starting slots?

It's a similar question to what I have for Guild Orders (some quests being use X of... something something), but that's not Tower Quest, so I'll leave it at that here. Unless you're curious about Guild Orders too.