Complete the game on Normal difficulty to unlock Muramasa's prize shop, artwork, and the Hard difficulty. Muramasa's prize shop allows you to view intermission sequences, letters, and character files that were found during your game session. Most are unlocked during the game by shooting the birds that appear when you use the microphone when a bird sound is heard.
In Chapter 5, "Legendary Fiends", there is an area in the Underground Mausoleum with a bridge and two Zombie Archers shooting at you. You will have to fight waves of Beetles if you fall from the bridge. Fall off the bridge and, as soon as you land, go to the back of the room at the right of the stairs. Charge your Ultimate Attack to red (repeatedly slide the stylus back and forth to charge faster than just holding it) and attack the Beetles. Collect the essence and charge the attack again, repeating this until all the Beetles are dead and you can go back on the bridge. Then, jump off the bridge again. Repeat for as long as you are in the Mausoleum. Note: If a Beetle attacks you before you charge, shake it off and roll to the other end of the area to charge. The Beetles ware slow so you can charge the attack without interruption.