All Characters
Go to "Collection", choose "Shinuki Cheat" and enter 4, 13, 11, 15, 2, 1, 14, 6.
Hints
Unlock Hidden Characters
Basilicum - Password: 1,7,14,16,5,12,10,3
Chikusa - Beat the Arcade Mode with Gokureda
Didi & Zizi - Beat the Arcade Mode with Lambo or I-Pin
Hyper Dying Will Tsuna - Beat the Arcade Mode with Tsuna
Ken - Beat the Arcade Mode with Yamamoto
Lancia - Beat the Arcade Mode with Mukuro
M.M. - Beat the Arcade Mode with Bianchi
Mukuro - Beat the Arcade Mode with Hyper Dying Will Tsuna
Squalo - Beat the Arcade Mode with Basiliscum in Hard
All the Cards
To unlock all the cards finish the Arcade mode with all the characters and the Family mode in the three dificulties.