Figaro no Kekkon
Figaro no Kekkon: Tales from Desert is a pamphlet written by Kaori Tanaka, a former graphic designer at Square. It told the backstory of Sabin and his brother Edgar, and explored their past in Figaro Castle. Tanaka stated in an insert that the pamphlet should not be considered canon, but I think it's likely she inserted that to avoid legal issues from Square. Tanaka was the designer who created Sabin and Edgar (as well as Relm, Duncan, and Vargas), and she had a detailed past and story planned out for the characters.
In general, there are often many things that aren’t used in games. I used to think all the story must be told, but these days I feel there should be room for viewers’ imagination.
A lot of the details surrounding Sabin in Final Fantasy VI are left up to viewers' imaginations; I've even included my own thoughts explaining what I thought were Sabin's motivations for various relationships and decisions on this site. Because Figaro no Kekkon was written in a time where Tanaka thought everything must be told, however, a lot of what was left up for interpretation was explained (in a non-canon sort of way ;)).
Because the doujinshi is extremely rare, I have not had the opportunity to read Figaro no Kekkon myself. Researching the pamphlet, however, I was able to learn many interesting details regarding the Figaro brothers, particularly Sabin.
Tanaka said in an interview that she loves deserts. When the character designers were dividing up the characters to create stories for, she took the machinist and monk. Her love of deserts led her to make Edgar and Sabin "kings of the sand." Making them royalty led her to give the brothers a couple unique character traits: in Figaro no Kekkon, Tanaka wrote that blue eyes are a sign of royalty in Figaro, and that all members of the royal family kept their middle names a secret. That explains why Sabin's middle name isn't mentioned until the end of the game. Revealing a middle name is a huge thing to a Figaro. It would require a lot of trust, respect, and probably love. In the Figaro no Kekkon stories, Sabin reveals his middle name to Cyan and Gau.
In the Cyan and Gau sections on this site, I wrote that I suspected Sabin viewed Cyan and Gau as family. Cyan and Sabin both lost loved ones to the Empire and were able to bond because of that. Gau and Sabin's bond was familial, too, as Gau didn't have anyone else. The three needed each other. In Figaro no Kekkon, my ideas are confirmed. Tanaka wrote that Cyan recently lost his son, and that Sabin and Gau had both lost fathers. The three really were like family. The fact that Sabin revealed his middle name to them and no one else shows just how close they were.
Edgar and Sabin's strain is also explained in the pamphlet. Even though the two should have been the most like family out of the Final Fantasy VI characters, they had a lot of shadows in their past to overcome. I think that if Final Fantasy VI had a sequel, or if the story kept going, we'd see that Sabin and Edgar would have gotten closer. Unfortunately, though, their relationship is one that would require a lot of work before that. Edgar still had issues regarding the night their father died and how he tricked Sabin. Sabin and Edgar had also been separated for years. In the pamphlet, Edgar wants what's best for Sabin like in the game, and that too is explained.
According to the pamphlet, Sabin had an unspecified genetic disease that he and his grandfather shared. It made him weak and sickly. That's why Sabin went to train with Duncan. He wanted to become stronger. Sabin trained with Duncan well before he left Figaro, though; in fact, Duncan trained Sabin twice a week since Sabin was eight. I guess that made Sabin feel stronger, and maybe less cautious, but his sickness still caught up with him despite his training. Edgar and Sabin played by the beach the day before they went on an antlion hunt, a Figaro rite of passage, and Sabin grew feverish during the hunt. They caught the antlion, but Edgar felt ashamed for how he treated Sabin. I guess that's when Edgar started watching out for Sabin, like a father would.
Sabin and Edgar's own father looked down on Sabin because of his disease, so it's easy to see why Edgar would feel Sabin needed someone to watch over him. If his own father wasn't going to, who else would? I said in the Parents section that I think Sabin and his dad were close. Learning about Sabin's disease and how his father looked down on Sabin because of it changes my stance. I'm not going to change the page since Figaro no Kekkon isn't canon, but it does make me think differently of their relationship. I think perhaps that Sabin idolized his father and wanted to be the best he could be to gain support from him. He probably thought his father could do no wrong and that the problem was himself. It's really sad, but that explains so much in the game. It explains why Sabin wanted to leave Figaro, because he thought so low of himself and thought his brother would be a better king. It explains why Edgar possibly felt indifferent (as he showed no emotion) after their father's death, and just worried about Sabin.
Figaro no Kekkon answers so many questions about Sabin and his past. I don't know where to find a copy (or I would have read it myself by now :P), but you can read about it more here at The Final Fantasy Wiki. Additionally, there is an interesting interview with Tanaka here that I quoted from in this section.