Josef 'Sepp' Freiherr von Brandt (né Josef Hauser) is the husband of Helene von Brandt. He is a Kapitänleutnant in the Wehrmacht's Kriegsmarine, where he worked as an ace U-boat captain. Outgoing, loyal, sensitive, and highly persuasive, he is a natural-born leader full of passion and charisma. He is known to be something of a 'father to his men' thanks to his strong values and love of people.
Sepp is a Baltic German from Riga, Latvia, just like the Von Brandts. However, he does not come from landed nobility. He grew up as a wealthy commoner. He met Helene at a Wehrmacht ball she was hired to play at. Helene's first impression of Sepp's engaging nature was that he was 'mad, bad, and dangerous to know'.
They courted for a year and married shortly after. Helene's father, Erich, was hesitant at first to see his daughter married to a non-Army man, let alone someone not of noble birth. However, he came to love Sepp as his own.
Due to Sepp's commoner status and Helene wishing to preserve her high-born heritage, they had a 'left-handed marriage'. Sepp took on the Freiherr von Brandt title, despite all nobility no longer having any sort of legal status in the Reich.
Sepp fathered twin girls with Helene, named Minna and Marcella. He raised them as best as he could in the midst of all the war-time madness. When Sepp discovered his wife collaborating with the German Resistance, he was furious at first. However, her invitation to have him watch her Polish-Jewish colleague perform Chopin's music changed his mind. He, along with Helene, helped some Poles and Jews hide from persecution by shielding them in their secret cellar.
When Sepp got word of the advancing Red Army, he quickly underwent Operation Hannibal, where he tried to evacuate his wife and children along with his unit.
When the ship they boarded, MV Wilhelm Gustloff, got torpedoed, it left Sepp and his family hanging off the side of the sinking ship. Unable to bear his family freezing to death in the cold Baltic Sea, he said his "I love you's" and goodbyes to his family. He shot Helene first, then Minna and Marcella. Sepp ran out of bullets when he put the gun to his own head. Alas, he slid after his dead wife and children across the icy, snow-covered deck, and over the side.
The remaining members of the Von Brandt family, Vinz and Alex, memorialized their deceased love ones through a piano and violin composition they wrote together, called 'Elegy for the Lost Souls of the Baltic Sea'.