By meeting a number of tasks in the game, you can make MegaMan change colors. This in particular affects how other people perceive you as well as affecting various shop and upgrade prices.

Unlockable	How to unlock
Dark MegaMan (20% increase in price at shops, most sidequests disabled)	Kick the pig at Calbania repeatedly.
White MegaMan (20% discount at shops)	Donate 1,000,000 Zenny to the Yosyonke church in one lump sum; 2,000,000 Zenny if you're Dark MegaMan.