v.148 - Grand Athenaeum Update Notes

My Dual Blade is the most, wtp, out of them all though. He's capped at 50% minimum (20% base, 25% Sharpness, 6% Hayato card, 10% Critical ring), but his maximum is at 76%(!) without the ring, and 86% with the ring. I don't even know where he got all that maximum from because Dual Blades don't have any maximum boosting skills.

My Battle Mage is in the same boat as your Dual Blade.

50% minimum and 61% maximum despite having zero maximum critical damage boosters, only minimum (20% base, 20% Battle Mastery, 15% Staff Expert, 6% Hayato Card).

Battle Rage (another 15% minimum critical damage) boosts my maximum critical damage to 76%.

Seems that your minimum critical damage's max is dictated by your maximum critical damage.