The Darksaber is a legendary weapon forged by the first Mandalorian Jedi, and has been at the heart of later seasons of The Mandalorian. The weapon was originally introduced on the animated series Star Wars: The Clone Wars before it returned on Star Wars Rebels. The weapon is said to entitle whoever wields it to rule Mandalore, but it takes more to wield the Darksaber than simply picking it up.
As Din Djarin learned on The Mandalorian's Season 2 finale, the Darksaber must be won in combat in order for its wielder to be considered the blade's rightful owner. Many fans suggested the introduction of this rule contradicted events seen on Star Wars Rebels, on which Bo-Katan accepted the weapon as a gift and went on to lead Mandalore with it. While The Book of Boba Fett would later clarify how Bo-Katan's previous ownership of the Darksaber came to be seen as illegitimate, the requirement for it to be won in combat had been confirmed long before she ever held it.
Sabine Wren was Told the Darksaber Must be Won on Star Wars Rebels
Star Wars Rebels Season 3 saw the young Mandalorian Sabine Wren come into possession of the Darksaber. After the Ghost crew had encountered Darth Maul in his lair on Dathomir, Sabine noticed the Darksaber among his trophies and took the weapon with her. Although she was initially reluctant to use the weapon or accept the responsibility that came with it, at the urging of Mandalorian Protector Fenn Rau and her rebel allies, Sabine started training with the Darksaber. She would eventually return to Mandalore with it to attempt to win the support of Clan Wren in the fight against the Empire.
Sabine's family members were surprised to see her wielding the Darksaber upon her return home. Her mother, Ursa Wren, feared for Sabine's safety while she held the Darksaber. Ursa asked Sabine how she came to possess the saber and Sabine told her that she took it from Maul. Ursa was shocked by this, asking Sabine if she had bested Maul in combat. When Sabine admitted she had taken it without defeating Maul in battle, Ursa told her daughter that she had no true claim to the Darksaber if it had not been won.
The Darksaber's Lineage on Star Wars Rebels and The Mandalorian
The interaction between Sabine and Ursa in Star Wars Rebels made it clear that the Darksaber cannot be held by anyone -- it must be won in combat in order for its wielder to claim rightful ownership of it and rightful leadership of Mandalore. Season 4 of Star Wars Rebels opened with "Heroes of Mandalore," a two-part story on Mandalore that concluded with Sabine giving the Darksaber to Bo-Katan, recognizing her as the leader Mandalore needed. By this point, it could be argued Sabine had won the Darksaber in combat, having defeated Gar Saxon after he stole the weapon. However, Bo-Katan never won the weapon from Sabine and thus had no true claim to it.
While Sabine gave the Darksaber with good intentions and viewed it as a reflection of the fact Bo-Katan had proven herself a worthy leader, other Mandalorians felt differently. Instead, they came to view this illegitimate claiming of the Darksaber as the action that ultimately doomed Mandalore. Season 3 of The Mandalorian saw Bo-Katan finally become the Darksaber's rightful owner. Ironically, soon after being recognized as leader of the Mandalorians, Bo-Katan came to realize the Darksaber was never what made her a leader and her right to rule was not dependent on it. The ancient weapon was finally destroyed in her conflict with Moff Gideon, but Bo-Katan has remained leader of the Mandalorians as they sought to rebuild their fallen home world.