Just play through With Knives from the first stage to the last, on Average Joe difficulty. To speed things up, you can use the power of love sword.
If you want to be max level before starting and don't have the money to move over from another character, you may also use the Konami Code Money Trick as described in This Thread until you have about $700.00 and then pay off Scott's Late fees in No Account Video and level Knives up (buy 'Seven Shaolin Masters' 10 time and then 'Alone and Disturbed' until you are level 16), before starting again from the first stage.
Power of Love sword unlocked at any stage
at the Title Screen