Shortsword of Daikokuten

Shinji Harukaze holds a tantō, which he initially thought it was a regular shortsword. The sword was given to him by his father, passed down through his grandfather, who was once a very famous ninja in his time.

It was later revealed that by Miaka Sakuragi that is was the Shortsword of Daikokuten (大黒天の短剣 Daikokuten no Tanken).

While the effects and powers that the sword holds or that it grants to its users are unknown, it is known that it is legendary and that it holds great power.

Trivia

 * Daikokuten (大黒天) is the Shintō god of merchants and fishers. This is why, before the sword was passed down to Shinji, it was a good luck amulet in Shinji's grandfather's small store.