Crocea Mors

It's a hand-me-down. My great-great-grandfather used it to fight in the war.

Crocea Mors is Jaune Arc's signature weapon. Jaune states that it was passed down from his great-great-grandfather, who used it in the Great War.

Description
The sword itself is a simple arming sword with a blue handle and a golden cross-guard. Jaune can transform the sheath into a heater shield for combat. The shield is white with a gold trim, displaying Jaune's golden emblem in the center.

His explanation for the shield's transformation is that when his arm gets tired of carrying it, he can shrink it down. However, when Ruby Rose points out that it would still weigh the same, Jaune sheepishly concedes the point. The shield appears to deploy with significant force, enough for its tips to embed themselves in a wooden doorway in "Jaunedice".

Both the sword and shield are shown to be incredibly durable, despite apparently being forged several generations prior to the present day. The sword is sharp enough to decapitate an Ursa Major, and the shield is sturdy enough to withstand several direct blows from an Ursa, a Death Stalker and Cardin Winchester's mace with no apparent damage.

The sword itself has several nicks on the blade and a few scratches and the shield has several scratches on it.

Upgrade
In "The Next Step", Crocea Mors and Jaune's armor were upgraded using either the broken remains of Milo and Akuo; the weapon of the late Pyrrha Nikos, her circlet or both. The upgrade was made by the blacksmith of a village in Anima as a form of payment for Team RNJR defeating a Geist.

The sword now has a heavier and more elaborate cross-guard and hilt. The shield is now accented with gold, including a design similar to Pyrrha's circlet at the point of the shield. The scuffs and scratches on both have also been mended, and the sword's blade has been polished to a new shine.

Due to the modifications, the sheath now possesses the ability to become a wider blade for the sword by extending the sharpened edges of the shield. Doing so adds the weight of the shield behind his blows, increasing the force of his attacks.

Trivia

 * Crocea Mors is Latin for 'yellow death' and the name of Julius Caesar's sword in some legends. Appropriately, the same legends have it becoming embedded in a shield.
 * Before its name was revealed, Crocea Mors was called Sword and Shielth. Jaune's voice actor and writer of RWBY, Miles Luna, acknowledged the name created by the fans and used it during the interviews before Monty Oum decided to reveal the true name of his creation via Facebook.
 * The old blade had the same design as the sword used by the male Huntsman on the statue in Beacon Academy that features a Huntsman, a Huntress, and a Beowolf.