To unlock a new difficulty for the two main tournaments of the Thousand Arena mode (Battle Royale & One To One) named "Shin Sekai difficulty" (Very Hard), complete the tournament in Grand Line difficulty (Hard) with 5 different characters.
Unlock the following characters by performing the corresponding tasks:
CHARACTER - HOW TO UNLOCK Chopperman - Finish the Thousand Arena One To One in any difficulty with the 45 characters. Main character support versions - Execute all the character moves in Training mode or finish a Thousand Arena tournament with the wanted character. Neptune - Connect to the Nintendo WFC and select "Download Content" to unlock a secret level in Story Mode. Finish this level to unlock Neptune. Shirahoshi - Connect to the Nintendo WFC and select "Download Content" to unlock a secret level in Story Mode. Finish this level to unlock Shirahoshi. Soldier Docking Emperor - Finish the Thousand Arena Battle Royale in any difficulty with the 45 characters.
The 1 VS 100 challenge is made up of100 short fights in which you are alone (without support characters) and cannot recover between each fight (for every 10 characters defeated you'll be rewarded a piece of meat). This is a tough challenge that demands plenty of concentration and coordination along with luck. To unlock it, you have to finish the Thousand Arena Battle Royale and One To One challenges in Shin Sekai difficulty (Very hard) 5 times each with different characters.