Hold Start + Select during game play.
Have a saved game file from Samurai Warriors on your memory card to start with all characters unlocked.
Alternate Musou attack:
When your Musou meter is full, press Circle to begin the attack. Then. release Circle and press Square rapidly. Your character will stop their regular Musou attack and hit the enemies with stronger versions of their charge attacks. This is especially useful with characters such as Nobunaga, that have erratic Musou attacks that only work against large groups.
Successfully complete the game to unlock that character's alternate costume.
A green cursor around your character at the character select screen indicates that specific character is a "lucky" character. These characters can receive there fifth and sixth level weapons one difficulty below the supposed setting. Note: Every time the game is turned off and restarted, the cursor will randomly change to another character.
Play the Battle Of Komaki-Nagakute as Honda Tadakatsu. Win all the missions, then defeat the supply team when it appears.
Play any versus mode option at least 35 times.
Tadakatsu Honda: Fifth level weapon
In story mode on his third mission, take out Oyamada to complete the first objective. This will make Ieyasu go into the crane formation. Afterwards, Shingen will order the Takeda cavalry to charge out. Do not kill any of the cavalry generals. Allow the cavalry to shatter the crane formation. This will cause Ieyasu to order a retreat, but Tadakatsu will decide to kill Shingen himself. After two or three minutes, a supply unit will appear at the lower right gate and move north. Kill the unit to get Tadakatsu's fifth level weapon, Arahabaki.
Fight against Lu Bu:
Get to floor 30 in the Abyss in survivor mode. Lu Bu may also challenge you if you surpass a certain amount of gold in Gold Rush in survivor mode.