How do I kill giant enemy crabs?

Solution 1:

You must attack its weak point for massive damage!

To expose the weakpoint on the Giant Masho Crab, you first want to destroy its pincers and afterwards his 'skull-face', revealing its Mashogane crystal, for heavy damage. Also, you can use Benkei's fully charged R1+Triangle to knock the crab over on its back and jump on it with Yoshitsune to "attack its weak point for massive damage" with R1+Square

During the battle, you want to avoid getting hit by his pincers or his charge attack, and also avoid the Masho Generals.

Now, for the (small) Masho Crabs, the easiest way to defeat them is to use Shizuka's wide sweeping attacks to get lots of Mashogane pieces, or to use Yoshitsune's Aerial Juggle Trick (Jump, Circle, 'Aerial Combo', repeat).