Once you finish the game with all 6 Title Screen Star Marks, you'll receieve an E-Mail from Solo telling you to level up the 4 In-Game Brothers. The 4 In-Game Brothers can be leveled up by doing their Side Quests. Once you're done with the Side Quests, finish the game once again. A New Epilouge will commence at the end of the Credits. Instead of Solo bringing you to Kodama Town, he'll be his alter-ego Burai and bring you to the Nansca Ruins. He'll want challenge you to a Wave Battle. You'll be able to take control once more, just so you can configure your setups before the fight. Talk to him and the Battle will commence, BuraiSX will have 3500 HP.
After the Battle is Over, you'll receive a Congratulations Picture on Both Screens with all the Voice Actors for the game saying "Congratulations" and laughing having a good time.