This playable character becomes available by doing the following. Start a battle and selecti Karin at the 'Character' selection screen. Then select Taka Sasuke (Akatsuki Sasuke) and wait for the time limit to end for the game to automatically select Sasuke Chidori True Spear as your character.
Earn 600,000 storm points by winning battles and then a pop-up will appear it will say: you have unlocked character: Lars Anderson and then go to free battle mode on main menu and Lars Anderson will be on the character select screen.
Connect two controllers and select Free Battle mode and play single matches against player two. Change the handicap in your favor and use Hinata's Y, B Chakra Ball move to do a 50+ combo. Then use your Ultimate Jutsu which is (Y(3), B) to get 10,000 SP per fight. These battles can be done in less than 20 seconds and they give you easy Storm points.
Complete the game and then return to Mount Myoboku and go up the stairs to the house. Then pray at the statue inside to unlock the alternate costume. You must have the Hokage Naruto costume to get the 'All Ninja Assemble' Achievement.