Isshin Kurosaki's sword "Engetsu" is a unique Zanpakuto with an interesting background story in the Bleach anime/manga series.

According to the story, Engetsu is an ancient Zanpakuto that has been passed down through generations of the Kurosaki family. It was originally wielded by Isshin's great-great-grandfather, who was a powerful and respected Shinigami.

Engetsu's unique ability is to generate flames that can be used for both offensive and defensive purposes. It can also transform into a more powerful form, known as "Final Getsuga Tensho," which grants the user immense power at the cost of their Shinigami powers.

The story of how Isshin obtained Engetsu is revealed much later in the series. It is revealed that Isshin was once a high-ranking captain of the Gotei 13, but he gave up his powers and went into hiding after a battle with a powerful enemy. He then took on the name Isshin Kurosaki and lived as a human in the world of the living. However, he continued to keep Engetsu with him as a reminder of his past as a Shinigami.

Overall, Engetsu is a powerful and unique Zanpakuto with a rich history in the Bleach series, and it has played a significant role in the story of Isshin Kurosaki.

Overall Length: 103.5 cm
Overall Length out of Sheath: 97.5 cm
Blade Length: 65 cm
Blade Width: 2.5 cm
Guard: 4cm
Material: 1035 Carbon Steel Blade 
Sheath Material: Wood
Sharp: No