I'm so awful at this game that I can't even A-rank 8-2 with Zelda to access the Great Fairy square. I'm not too concerned with unlocking level 3 weapons, heart containers, or Gold Skulltulas, but I want access to every base weapon, and the Great Fairy is eluding me.
I've only been playing this game a few weeks, and that part stonewalled me for a while, but I ultimately A-ranked that mission (to get the lv. 2 baton) by using the Guard Break potion, and Zelda's Dominion Rod (DLC -- I take it you downloaded?).
Lightning is recommended on that stage, but the Dominion Rod makes quick work of captains. Start a weak attack string until the statue starts popping out of a portal in the ground; this juggles the enemy captains; and then dodge-cancel out of it before it finishes, and repeat.
Once you buy the Guard Break potion, it's in effect for the entirety of whichever mission you do next. It's worth it. You'll deal damage against those pesky flying lizard-men (I know how to say their names but not how to spell them). You want to quickly dispatch the first one, right at the start, then immediately run to the area in front of the Fairy Fountain (the Allied Base). If you're fast enough, you can catch Volga while he's still in the keep to the east of the Fairy Fountain; defeat him in the keep and you'll capture that keep to better protect the Allied Base.
Volga will also drop a Magic Jar. Grab it and use it on Wizzro, who's approaching the Allied Base from the northwest. Just go into Focus Energy and use a Special Attack to instantly reveal his Weakpoint Gauge. Wreck him with the Dominion Rod and head straight for the keep to the west of the Fairy Fountain. Start cleaning out the keep, and if you're quick you'll capture it before the rogue commander (another flying lizard-man) arrives. You might even be able to make a quick beeline up the canyon to the west, heading through the keeps in the northwest, and destroy the summoners -- one in the keep to the northwest, IIRC, and another on the altar in front of the commander in the northernmost keep.
Once the rogue captain is dispatched, the Enemy Forces send reinforcements. If you take just a little bit of time to winnow their numbers as they pour out of the altar, you can approach 1,200 KOs. You can also keep your KO count afloat by keeping the keeps east and west of the Fairy Fountain in the blue, which also protects the Allied Base (located in the Fairy Fountain).
When running for the commander of the Enemy Forces, in the northernmost keep, take the northwest canyon and crack the green pots along the way. By going into Focus Energy and using a Special Attack on Ghirahim, you'll automatically reveal his Weakpoint Gauge. Coupled with the Guard Break potion, you'll wear him down quickly, and while fighting him, you'll take out stragglers that should put you over 1,200 KOs.
Watch out for the heavy Moblins, and spam dash when Volga turns into dive-bombing dragon form. I find I take most damage from those two.
I hope this helps. Like I said, I made much more progress with the Dominion Rod and Guard Break potion. My Zelda was in the 40s, I believe.
The mission for the Great Fairy was much easier by comparison, I recall. The lv. 2 baton mission is definitely one of the harder ones.