This can be difficult if you are:
a) Under leveled (I was at 15 with each char except my golem which was a level 20, name was Spooky something, had gravity and EP drain)
b) Don't have the haxor golem that can be acquired early in the game at the casino or something like that (Marlin Glave)
My advice, level up as much as needed, and attack, ALWAYS attack the golems he summons, if 3 are summoned, he unleashes some powerful attack. He almost always stands behind them, so use Atsumas Wave skill, Reigers Slash (I think that's it's name, the attack area is a plus shape, this will hit the golem and Kou.), and Karins various water attacks, these work pretty good as they inflict damage to all golems in that 3 square area. So, don't focus on Kou, much easier to focus on killing golems, and, if your lucky, Kou will behind the one you're attacking.
I hadn't played this game for at least 6 months cuz I was stuck at this part, I played it last week, and got it on my first attempt. There's a bit of luck involved.
Also make sure to have many HP and EP healing items, have Reiger use his Barrier skill, and always revive if needed with.... Karins rev skill.
Takin' From Enchanted-Arms.com
(Credit to LM)
5. London City (NOTE, LONDON CITY, READ ALL THIS BEFORE YOU ADVANCE TO FAR, OR YOU'LL BE SORRY)
After some conversation, you'll be able to control Atsuma again. Now head out from the Tavern. There's a Refresh Terminal and Shops here. Stock up if you want. There's a casino here. Now, this is the time to decide how do you want to PLAY your game. If you wan't to cheat, then read on. If you want challange, then i suggest you to skip this section. But i do suggest you to bet until you have enough to get Marlin's Glave golem. You're going to need it !!
Marlin Glave is your friend (791 HP!! :O)
The game will be a LOT easier if you have it in your party. Trust me, a golem with 700+ hp couldn't be wrong :D
Ready ? OK. Go enter the Casino. You can start by buying 1000 chips. If you don't have enough money to buy that much, its alright. Just buy as much as you can.First you need to build up your chips. Now you need to put your bet on either ODDS or EVEN. If you put 1000 CHIPS, you may get 2000 chips in return when you win the bet.If you lose, RESET.
When you have enough chips to play "big" (i suggest around 20.000+ chips) put 1000 chips each on number 15-20 (you can use different combination of numbers if you want, but let's just use these numbers for example).If you hit either of them, you'll get 36.000 chips in return !!!! Now start your bet and pray that it will on either of those numbers. If you keep losing, just simply reload your game. When you get at least 200.000 chips, you can stop since it'll be more than enough for now.
Put 1000 chips each between number 15-20
Ok, now you have 200.000 chips in your hand. What should you do ? Simple, just change all your chips with the prizes...and you'll still have plenty of them left ;) See the Recover Powder over there ? It won't run out, and you can sell it at the store for 600 each !!! You can buy 9 maximum per trip, so that makes it 5400 per trip. Repeat the step above and you can have unlimited money and unlimited SP because SP can be purchased at the shop!!! This is a perfect time to fuse your golems, improve your character's stats and skills.