One Piece: Gigant Battle 2 - Shinsekai Hints & Cheats

You can 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). To do that, you have to finish the tournament in Grand Line difficulty (Hard) with 5 different characters.

The 1 VS 100 challenge consists in a serial of 100 short fights in which you are alone (without support characters) and not being able to recover between each fight (except that after beating 10 characters you'll be rewarded a piece of meat). This is a hard challenge which demands a lot 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.

Here is a list of characters that can't be unlocked through Story Mode.

To unlock Robin, Franky & Brook pre-timeskip's second support attack, you must level them up to level 3 in Story Mode. Robin's second attack is "Wing", Franky's is "Ballad" and Brook's is "Yahazugiri".