Enchanted Arms

This is a story-related boss battle again against Ooka. The only party member you will be able to use is Raiga. As PhotonQyv said, you can use Raiga's EX skill to double his stats, making it a much easier fight.

In preparation of this boss battle I would advice in using Raiga in some previous battles. If you do not get enough SP and invest it in some skills you will be stuck with only his starting Blade attack (and EX attack). This can be a big problem if Ooka does not stay on the front row.

A good attack to invest in this battle is High Earth Shake (buyable at the shop). Ooka is wind type and is thus weak to earth attacks. (It also has one more range than Blade.)

For even more range the Slash attack can also be useful. You will get this during story progression.

Since it is story-related you can't miss it. If you're feeling a little under-powered try your character's EX skill on the first turn, accept the hit and then take the offensive.