I begin this video from a saved game at chapter 6.3. This is right after you get the Vandal heart sword and your raid back on the occupied capital. I defeat Xeno and Both forms of Dolf on this run, including clearing all of the other enemies on the battle field just for fun.
All of my characters are at level 49 which makes the process quite easy. This was done through the leveling up process and is not a cheat code but rather a mathematical glitch in the experience point allocation system of the game.
You can exploit this in the following manner:
As a general game rule if a person performs an action on a higher level enemy he gains more experience than if he performs the same action on a lower level enemy. However if a character performs an action on himself he gains a set amount of experience regardless.
In order to capitalize on this you will need one of your characters to have the Mystic shield spell which accompanies either the healer or monk class. The odd thing about the mystic shield spell is that you do not get experience point for using it on other people, however you always get 16 or 17 experience points everytime you cast it on yourself. The spell is cumulative so if you cast it so many times in a row you can level up by yourself with the only cost being 3 MP per spell.
The name of the game here is the relative difference in levels. To capitalize on this spend all of your money buying mage gems and mage oil and equipping those on all of your characters. Have your healer always cast mystic shield every round that you can until he runs out of MP. Then have the healer use the MP replenishment items on himself first to boost his own MP (also experience points) and then use more spells until he is out again. Then move a character next to him and have the character give him an MP restorative to boost the healers MP and also level the giving character up for performing an action on another character. The beauty here is that the healer will almost always be at a much higher level than the others so the experience gained will increase greatly. I have had a character gain 30 levels in one go before by getting 3099 experience points by the difference in levels.
During the time you are doing this you will need to be on a field where you can paralyze enemies or even better be on one where you have to take your whole party to a certain place. In the later instance you can kill all the enemies and then just waste turns leveling up in this manner before moving to the designated spot and ending the board.
At a certain point the levels will taper off as the character reaches close to level 49. At this point you will want the healer (who is most likely either a ninja or archbishop at this point) to just cast a spell or two so that the remaining characters can just give them mage oils to continue their level up process. As you near the top your character, giving mage oil to a level 49 healer will have to give them one mage oil to get 100 Experience points at level 46, then one more to get 66 Exp to get to level 48 (because of the extra from the previous level, and then 3 mage oils to get to level 49 at 33 experience points each. Make sure you purchase a lot of mage oils before leaving the town at chapter 4.1 because this will be the last time those are sold and you will have to use mage gems which are $1100 more a pop.