I think I just figured out how to bring Midoriko's Luck-based skill activation rates to 100%.
Mozume!Midoriko has a neutral Luck modifier (+0). This is unfortunately as high as she can go (without Kamui as a mother), but it will do.
If Midoriko marries Kisaragi or Shigure, she can reclass into Golden-Kite Warrior via Marriage Seal, bringing her Luck cap to 34.
She can wield bows, like Anna's Lucky Bow (which grants Luck +5). Luck becomes 39.
If Mozume A+'s Oboro, reclasses to Basara, and builds up an A-support with Midoriko, then Midoriko's Luck becomes 45 when paired up with her mother, Mozume.
Midoriko equips the skills Flamboyant (obtainable through inheritance via Mozume's A+ with Oboro), Hoshido (sadly only available through the Logbook in this case), and Luck Drain (DLC). Together with her personal skill, Lucky Charm, Midoriko's total activation rate shoots up to a whopping 90%.
And when she kills 5 enemies, it climbs even higher to 100%. This is perfect for skills whose activation rates are based around Luck: they will always trigger.
On that note, does damage from Extravagance stack?