No More Heroes III: The Official Companion Guide

Beat the game once on either Sweet or Mild difficulty to unlock Bitter mode. All of your stuff from the first playthrough will carry over, including your various clothes, money, techniques and purchased weapons. Only in Bitter mode will you be able to get your grubby hands on even more cool stuff, such as extra parts for Tsubaki Mk-III and character concept art in the form of the collected Trading Card No.'s.
T-Shirts and Extra Cash
This isn't so much a secret as it is a heads-up of sorts. Located around the city—usually in alleys or parking lots—are dumpsters that can be kicked open. Within most of these dumpsters, Travis will dig up an old shirt that he will immediately don and then add to his growing collection of oh-so-cool tees. Other times you rake in about LB $2,000. You could also press A in dirt areas to unearth money if you are lucky.
True Ending
Once you've attained rank number one, start a new save file with your new data. If you do not have the option to view the True Ending, it is simply because you did not purchase all the weapons available for purchase from Naomi—three in total. Naomi's latest creation, Tsubaki Mk-III, will run you LB $498,000, so get to saving that dough.