Denkomaru is Issun's trusted yet tiny sword. Although it appears to be quite weak because it it only the size of a pin Issun uses it to open the mighty Spirit Gate. He also uses it to damage enemies and steal their Treasure when Amaterasu uses Thief's Glove and with the proper practise Denkomaru can take down enemies with only one strike.
Denkomaru is the sword made from a needle that Issun Boshicarries in the fairy tale. He uses it to chase away an Oni thus earning him the hand in marriage of a princess.