another question: can you get ++ or higher blue passive skills?
Yellow or red? Skills go Base/Yellow+/Yellow++/Red+/Red++
From what I've seen: Passives can only go up to Yellow++. Attacks can only go up to Red+. Some support skills seem to be the only things that can go up to Red++. I've attempted to upgrade Healing/Noble Cross D Red+ to Healing/Noble Cross D Red++ approximately a million times and I've never been able to do it, so I'm pretty sure it's not possible.
Skills I've managed to get it Red++: Repentance Hall D, Divine Protection D, Full Boost D, Light Wall D, Bind D, Lunatic Waltz D, Bind A (Pretty sure most counters can go to Red++, I just barely use them so I haven't bothered trying to upgrade them).
Something else I tested is whether you need to have the defense deck selected when attacked for them to work: You do not. Using 4 Mystic Eyes of Fortification, which should reduce damage by 20%. Aquila always does Round House Kick, Flames of Judgement, Purge in that order unless you disrupt her skill cds, so it's stable for testing since the zone control damage you take is the same each attempt.
35% extra Zone Control protects you as much as Divine Protection D (20%) is something I found interesting. Weird part is that starting with Smile Flash to boost the starting Zone Control before the combo doesn't raise defense going from 62% to 72%. I get the feeling there are flat caps with Zone Control that boost defenses rather than it being a percentage boost. Finally see a defense increase at 77%, so one cap may be 75%.
Zone Control for the MC's damage:
How the fuck Zone Mastery works is anybody's guess since it's not displayed anywhere for whatever reason. I'm really curious about that but there's no way for me to test it reliably without numbers. It actually doesn't seem to do anything if used at the start of battle for the MC's offensive or defensive Zone Control. There's a chance the MC starts off with it maxed already and it only becomes useful later in battle? That would mean at the very least it's not worth leading with, and worst case scenario it has no effect on Zone Control gains/losses (The skill Repentance Hall could be bebugged as well).
Defense calcs are weird as fuck, and seem to include Zone Control early in the damage calculation, after all your passives/actives/counters are calculated. This means you can negate Zone Control loss with high damage negation. What's weird is that counters don't seem to work as well with passives as active abilities. I don't know how that works.
TLDR for all my testing so far: