Hard Mode is a game mechanic and seen frequently in the Fire Emblem series. Beginning with Fire Emblem: The Binding Blade, games offer a Hard Mode after the player has cleared the game once. In Hard Mode, there are usually more enemies, and they are more powerful, receiving a set number of hidden Level Ups.
In Radiant Dawn, the player had to first clear the game on Normal Mode in order to be granted access to Hard Mode. In the Hard Mode of Radiant Dawn, the Battle Save feature was disabled, and the player was unable to see enemy attack ranges on the map. Additionally, the weapon triangle and map affinities no longer applied.
In Shadow Dragon, there are five levels of Hard Mode, none of them feature the prologue, with hard available from start and more difficult versions are unlocked by beating the last, with the highest called H5, or Merciless. In H5, all enemies have weapon ranks of A, and their stats are insanely high. Some of them also have forged weapons. The sequel continues this trend, but with all levels available from the start, the prologue chapters still played through in a more difficult form, and even offering a permanent reward for completing any hard mode once: the ability for characters to reclass into any class of their gender, without restrictions.
In Awakening, most enemies get new skills and forged weapons. They can receive skills that their level cannot get at the moment (e.g a level 4 Warrior with Counter). Enemies after Chapter 21 will also begin to have forged weapons whenever possible.
In Fates, most enemies will have skills, with a few having access to skills that they cannot normally obtain. Enemy reinforcements are also stronger and can appear in chapters that do not have reinforcements on Normal Mode.
Regardless, in both Awakening and Fates, enemy weapon proficiency are better then that of Normal Mode. The minimum weapon rank proficiency for both games is C compared to E on Normal Mode. In addition, they will also be carrying higher ranked weapons; for example, enemy Onmyojis in Fates are more likely to carry weapons like Dragon and Snake Spirits compared to those in Normal Mode. In addition, skirmish training in Hard mode is harder due to the increased prices to create one.