Instructions
Play through Squall's part of the Story mode. When you complete this chapter, you are rewarded with the Revolver weapon for Squall.
Acquire three Spirit Stones and two Bless Shards. You can find Spirit Stones by fighting in the Air Ship level, or you can trade Dusty Elixirs for them in the shop. Bless Shards are Battlegen items that you receive by fighting Squall when he is Level 30 or higher. Trade these items and the Revolver at the shop to get the Twin Lance weapon.
Get five Goddess's Magicite and three Bless Crystals. You can acquire the first of these items by fighting in the Invincible Course, or you can trade Hi-Elixirs for them at the shop. Bless Crystals are battlegen items that you get by fighting Squall when he is Level 51 or higher. Trade all of these items and the Twin Lance at the shop to get the Punishment weapon.
Find five Bless Orbs and five Unshelled Bullets. As with the previous Bless items, you must fight Squall to get them. These are extremely rare, so your best chance of finding them is fighting Squall when he is Level 100. You can find Unshelled Bullets in the Duel Colosseum, or you can trade Megalixers for them. Trade all of these items and Punishment at the shop to get Lionheart.