Unlockables

Bonus Items - From the start button menu, there is an option to review checklists of certain aspects in the game to see how many you've completed. There's a similar option called the "Memo Pad" that lists the various side story missions such as bounties or employment. If you complete these lists, you will get bonus items. Most of them are sent to you by the postal service in the game, but there are a few which will simply be given to you by a character (e.g. completing the "Inventions" list will prompt the inventor to give you the item).

Best Dachi in the Realms (Tenka no Dachi) Techniques
Dragon Chestplate Weapons
Ganryuu Bokutou Arena Opponents
Immortal Turtle Yuujo (Pleasure District girls)
Lucky Beads Storage Lockers
Meow Shoes Inventions
Peerless Wakizashi (Musou no Wakizashi) Memo Pad
Seven Luck Dieties Sarashi Food and Drink (restaurant menu items)
Skanda Shoes Skill Games (includes gambling)
Ultimate Badge Heat Actions

Unlockables - After you complete the story mode, you get a bonus depending on what difficulty you selected. New modes open up, too. There's also a bonus item for getting "S" rank in every mission in the Ultimate Fighting mode.

100 ryou (1,000,000 mon) Complete Story Mode on Hard
30 ryou (300,000 mon) Complete Story Mode on Easy
50 ryou (500,000 mon) Complete Story Mode on Normal
Brawling God Amulet Complete Story Mode on Expert
Expert Difficulty Complete Story Mode on Hard
Galavanting in Kyoto (Adventure Review) Complete Story Mode
Reminiscence (Cinema Replay) Complete Story Mode
Start Game with Clear Data (New Game+) Complete Story Mode
True Brawling God Amulet Get "S" rank in all Ultimate Fighting missions
Ultimate Fighting (Battle Missions) Complete Story Mode