Main thing if you want to get Route C done fast: do the Recycled Vessel side quest. Is super easy to do, and is required to get Route C's ending. However, the main thing you want is the Fool's Lament weapon. If you finish the side quest, you get the three Fool weapons, along with three Damascus steel. If you have enough money, fully upgrade the Fool's Lament as soon as you can, All it requires is the three Damascus steel, and caps at 999 damage, the max amount of damage in the game. The weapon is Extra Heavy, but it plows right through all enemies and mini bosses, even main game bosses at times.