Izuna 2: The Unemployed Ninja Returns Codes -

Bonus dungeons:
Complete the main story line to unlock the following dungeons.

Girls Only Dungeon located at the shrine near Himiko
Mugen Chasm located where Shizune ran to.
No Item Dungeon located at Surei Town. The Gankatsu talisman is required. 

Bonus characters:
Complete the main story line, then talk to the following bonus characters at the indicated locations.

Gen-An
Himiko at Kamairi Village
Hinagiku at Mugen City
Ichika at Surei Town. You must first unlock the No Item dungeon.
Suzuri at Kamairi Village