Katana

The Katana is a moderately curved Japanese sword with a blade length greater than 60 cm. It is characterized by its distinctive appearance: a curved, slender, single edged blade, circular or squared guard, and long grip to accommodate two hands. It has historically been associated with the samurai of feudal Japan and has become renowned for its sharpness and cutting ability.

Etymology
"Katana" is the term now used to describe nihontō (samurai sword) that are 2 shaku (606 mm / 23.9 in.) and longer, also known as "dai" or "daito" among Western sword enthusiasts although daito is actually a generic name for any long sword.

Pronounced [katana], the kun'yomi (Japanese reading) of the kanji 刀, originally meaning dao (sword) or knife/saber in Chinese, the word has been adopted as a loanword by the Portuguese language. In Portuguese the designation (spelled catana) means "large knife" or machete.

In the Anime
The Katana used by Saya Otonashi in the anime, like other katanas, is a samurai sword of slender curved blade with the exception in edge. The edge is specially designed so that she can touch with her thumb while gripping it so as to draw blood, and grooves specially designed to spread her blood through its entire blade. Once loaded with her blood, it is a deadly weapon against Diva and any chiropterans created from Diva's blood. The katana is encased in a sheathe and carried by Hagi in his cello case when not used by Saya.

There are two blades used with the katana:
 * The first one comes from Joel Goldschmidt's armory and has been used by Saya Otonashi for ages until it breaks.
 * After Saya Otonashi's first blade is broken, David gives her a new one (at the end of Season 2) that has a red crystal at the base of its blade, symbolizing her membership in the Red Shield organization. The crystal is a piece of her adoptive father's body, which crystallized when she killed him with her own blood in order to spare him the fate of turning into a Chiropteran. With this blade, Saya keeps on fighting until the last showdown against Diva and finally manages to plunge the blade loaded with her blood into Diva's body, ending the feud once and for all. The last act of the blade is performed by Hagi when he uses it (still loaded with Saya's blood) to strike Amshel.