Hard Mode is a difficulty mode available in all of the Nicalis ports of Cave Story. In it, Quote must go through the entire game without getting a single Life Capsule to increase his HP (except for the one given to Quote by a dog in the Plantation). The Missile Launcher is also removed.
Quote's appearance changes in the mode too; instead of the normal red outfit, he wears a light blue outfit, and has blonde hair instead of black. His skin is also a peach color, instead of pale white. This gives him a more human-like appearance, but all character dialogue noting that Quote is a surface robot remains unchanged.
The game is the same in every other way. This mode is not available on the original freeware version of Cave Story.