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Death Note is a manga/anime series in North America. View Wikipedia article. This world will only become unlocked once you pay 400 purple gems on Ou Tenkun's evolution chart.

[edit] Mission One

1. Defeat all opponents. Doing this will unlock TODO.
2. Knock out an opponent by ring out.
3. Knock out two opponents by ring out.
4. Knock out three opponents by ring out
5. Win within 50 seconds. Doing this will unlock TODO.

[edit] Mission Two

1. Defeat all opponents. Doing this will unlock L.
2. Win within 40 seconds.
3. Win within 30 seconds..
4. Win within 20 seconds.
5. Unknown. Doing this will unlock TODO.