Sed is the mortal son of Seth Balmore who has physically aged beyond his mother. In his younger years, the notorious pirate Sed was always rough and ready for a fight. That passion hasn't waned as he's grown older, but his wisdom has caught up with his spirit, giving him a little more caution than before. Kaim and his crew finds Sed is quite grateful for the show of friendship. He's deadly accurate with a rifle, and his trusty ship is a fine way to cross the open seas.
It could be considered that Sed's name is derived from the Cid characters of the Final Fantasy series, as Hironobu Sakaguchi, the creator of Lost Odyssey, also worked on a lot of Final Fantasy games, where the name Cid is a recurring theme. This is further backed up by the fact he is the main mechanical member of the group, and provides them with vehicular transport, which is another recurring theme of Cid.