Sabian

 is a former crewmate of Fjord.

Background
Sabian was the one responsible for sabotaging the ship Fjord worked on. Fjord walked in on Sabian lighting a fuse, but before he could react Sabian wounded him with throwing daggers. Sabian then ran to the deck of the ship and jumped into the ocean. After surviving the explosion, Fjord returned to one of his contacts and learned that Sabian had also survived.

Captain Adella told Fjord that Sabian has recently been working with a shady merchant named Cadmus Leeland in Nicodranas. Leeland's ship is named the Widow's Embrace.

Campaign 2: The Mighty Nein
 Fjord talked to Mollymauk briefly about the explosion of the Tide's Breath and the possible connections to his new falchion.

 While the group spent some downtime in Zadash, Fjord went down to Trostenwald by himself to see if anyone had heard of Sabian or of the Tide's Breath. After returning to Zadash, Fjord confided in the rest of the group about Vandren and Sabian, and their possible connections to the sword.

 Fjord introduced himself to Captain Adella and asked if she knew anyone by the name of Sabian working for her. While she did recognize the name, Sabian does not work for her, but instead a man by the name of Cadmus Leeland, a lowlife pirate who passes himself off as a sailing merchant.

 Before leaving Rumblecusp, Fjord walked over to Kotho and asked if he could partake in a contract. He mentioned to Kotho that he wanted information on Sabian's current location.

Relationships
Fjord told the Mighty Nein he's known Sabian for many years, and they grew up together. Despite this, Fjord does not seem to have had a good opinion of Sabian even before the Tide's Breath explosion. It is unknown how Sabian feels about Fjord.