Welcome to Gaia! ::

You're going to want to complete every other quest and side quest in the game(Aside from the end, in which you lose the ability to have Atoli in your party. You don't really need her but she helps alot.) for a smooth fight against the doppleganger. Something I've learned is that without quest bonuses they manage to keep up with Haseo in damage and defense factors so long as you equip them right. Give all three of your party characters independent attention in customizing. While just slapping mantis nails on your weapons may sound like a good idea, your healer would need nothing on their weapon but if you have a special armor customization item, you would want to sacrifice it to your healer so the doppleganger will shy away from them. stocking up on healing items is important 25 revival medicines, 50 sprite drops, and 25 healing items (Serums are recommended but are relatively harder to acquire) all of which are a must if you can afford it. (I would just rush temples for the treasure and sell it off, going to an area where monsters fall in one or two hits is just fine for hoarding treasures.) Make sure to give all of your healing items to your healing character (DO NOT POOL REVIVAL ITEMS TO ONE CHARACTER, THIS WILL MEAN YOU'RE SCREWED IF THEY DIE, DIVIDE THEM UP RELATIVELY EVENLY)

The doppleganger is relatively simple to locate if you have the patience to wait ten minutes in any select area. If you see a red arrow pointing in any direction, that is where he is coming from. Head towards the arrow and when you hear an alarm and see your screen flash red you need to re-check your equipment and items to make sure you're ready, if not, re-read step 1. If you're ready, start the battle.

If you want an instant bonus (And perhaps a win) pick an area you know you can reach a beast awakening in three battles. (Level 50 area reccomended.) Don't worry about using items to heal, once you've gained enough moral for an awakening, you should simply stand still for the remaining time and allow your healing character to do the job without having to bother with using up items and this will also burn up some time for waiting for the doppleganger.

If you can, try to sneak up on the doppleganger and hit him with your steam bike. While this won't deal tremendous damage, it will help a little. You will want to use the dual swords for this because with the broadsword, the doppleganger isn't hit hard enough to knock him away from his skills. Stay away from your SP in this fight!!! Do NOT use the skill trigger until you can use a rengeki. The doppleganger heals automatically and it heals enough that no matter what skill you use it will be fully healed by the time you finish the skill. Build up your moral as fast as you possibly can to get a beast awakening. Once you've done that, unleash your pent up fury! Go full force, start the awakening with your strongest skill and don't let up. If you run out of awakening before the fight ends. Then still push. If he has more than half hp after your awakening, then attempt to keep him lower down than max and build up your moral once again. You should be able to take him down in the first awakening so long as you coordinate your other attacker's skills as well as your own. (Yes, this means you will be going in and out of the menu.) Once you've defeated him, you get the item "own king" this will allow you to receive one of the best weapons in volume two by defeating the doppleganger again. (Trust me, this is going to be alot easier with Atoli and a specific blue haired character that will not be named due to the fact that I wont be spoiling anything.) For those of you who went through the excess preparations, start the battle with an awakening.