After beating the game, you can add Kizamaro to your Brother Band. He grants MegaClass+1, HP boosts, and his final Brother Force selection includes TripSong, GravityStage, MagicCrystal3, CancerBubbleSP, WolfForestSP, and CrownThunderSP. To unlock Kizamaro, speak to him at the Denpa Udai in Kodama Town and then head to the school gym. Wave into the Piano network and speak to the leader Jamminger you find to begin a 10-in-a-row battle sequence. After you win, speak to Kizamaro again to add him to your Brother Band.