If you have obtained and have at least one use left on the following weapons, you will unlock three extra chapters, revealing the TRUE ending of the story.
Durandal
Armads
Malte
Miruge
Aurelora
Apocolypse
Forblaze
Holy Maiden
Sealed Sword

You also have to Fa, the Divine Dragon alive at the end of chapter 22, "The Neverending Dream." In these chapters you fight Brunya, Yahn, and Idoun.

To unlock certain chapters ([chapter nimber] X ) you must meet certain requirements. These chapters contain "S" ranked weapons as well.

These are as follows:

Chapter 8:
Requirements: Beat the chapter, and keep Lilliana alive.
Weapon: Durandal, The Blazing Sword

Chapter 12:
Requirements: Beat the Chapter in 20 turns or less.
Weapon: Armads, The Lightning Axe

Chapter 14:
Requirements: Beat the chapter in 25 turns or less, and keep Sophia alive.
Weapon: Forblaze, The Infernal Element

Chapter 16:
Requirements: Beat the chapter keeping Douglas alive. He is an enemy general, and will attack your units. Be careful, he can kill you and vice versa.
Weapon: Aurelora, The Pinnical of Light

Chapter 20 A/B:
Requirements: Beat the chapter in 25 turns, and keep Dayan/Yuno alive.
Weapons: Miruge, The Bow of Winds/ Malte the Frozen Spear

Chapter 21:
Requirements: Beat the chapter in 30 turns, bring Fa, and keep her alive. Also, have both Milady and Ziess talk to Gale, Murdock's DragonMaster leutenient.
Weapon: Apocolypse, the Silencing Darkness

In the begining of the game you pick (put) your birthday in. Well the affin you get when you chose the month is useful when you use units. Whatever you affin is ex:magic then you do better with other units who have the magic affin.

On chapter 21x (the one with Sonia) the only people she hits or tries to hit with boalting are lords nino and jaffar