Derflinger

Derflinger (デルフリンガー, Derufuringā) is an Intelligent Sword and Saito Hiraga's talking sword.

Background
Derflinger was created by Sasha, the first Gandálfr. It is actually a spirit sword, and upon the destruction of its form, it can transmigrate to a new sword body over a period of weeks. It also seems able to absorb magic from attacks cast at it, which it later uses to fuel its various abilities.

Six thousand years later, Derflinger is an item at a sword shop in Tristain, costing 100 gold coins.

Void Day
On Void Day at Tristain Academy of Magic, Louise de la Vallière and Saito Hiraga go to a local sword shop to buy the latter a sword. With its cheap price, Louise purchases it for Saito. Back at the Academy, when Louise and Kirche von Zerbst fight for Saito and force him to choose between their purchased swords, Derflinger awakens and calls the two ladies as "stupid women", angering them. Tabitha points the sword out to be the one that talked; this amused Saito, leading him to choose Derflinger rather than Kirche's grander sword.

Post-Void Day
The next day, when Saito heard of Siesta's departure to work under Count Mott, Derflinger and Louise brief Saito about the possibility for him requesting Siesta to become his mistress; coupled by his cocky personality, respectively, worrying Saito even more.

Fouquet Strikes
Louise prepares Saito for the upcoming Familiar Exhibition, but becomes hopeless at him. She recalls his swordsmanship skills upon seeing Derflinger, but he refuses because of his inability to do so at Mott's manor. Running out of ideas, Louise goes to class and orders him to think of something to exhibit. Saito attempts to practice his swordsmanship skills with Derflinger, but to no avail.

Later, Louise, Tabitha, Kirche, and Saito, along with Longuevuille, set out to capture Fouquet. Along the way, the enemy's golem appears and battles the team. Initially, using the sword given by Kirche, Saito attacks the golem, but the sword breaks. Derflinger advises Saito to use him, despite the latter's initial worry that he might break, too. As he draws Derflinger, Saito feels the same sensation and strength that he felt during his duel with Guiche; true enough, he was able to cut the golem, albeit it regenerates at the parts that were sliced. Ultimately, Saito defeats the golem using the Staff of Destruction; upon the reveal of Longuevuille's real identity and betrayal, Saito uses the hilt of Derflinger to attack and defeat Fouquet.

Later that night at the banquet, Derflinger notices Saito's frustration; the latter states that he almost had the answer to find his way back home. As Louise arrives, she asks Saito to have a dance with her. They have a dance, with Derflinger remarking that it is his first time seeing a familiar and his master dancing together.

Academy Summer Vacation
During the summer holiday, Saito borrows an old giant pot from Marteau. Derflinger asks what he shall do with it, but Saito merely gives him a hint that he shall use it later at night.

The next day, as they head to Lake Lagdorian, Derflinger exclaims that he quite recalls the Spirit of Water himself. Saito later uses Derflinger in battle with the hooded figures.

Quotes

 * (To Saito) "If you don't want to die, draw me!"
 * (To Saito) "There is no coincidence in this world. You are my partner, and that's why I'm here."
 * (Referring to Saito) "Hey. hey, partner! Although so much has happened, it seems to me that your relationship is developing quite well. But how long will this type of relationship last?"