At the end of the game after you beat the Stigma tranformation after the whole scene and your asked to save your game save it over your file (an empty file if you don't trust me)and you can play the game with the character levels you last used them with and if you had a lvl 38 Forte at the end of the game you get him at that lvl and you can keep doing that on and on (also same weapons but not accessories)
It takes a long time but when your lvl 50 and have a save file from LOH 1 you can just do God of Darkness in the sacred land and you fight Octum over and over till your lvl 100!!!Hope I helped!!!