"It's going smooth like butter because I am the smartest man in the entire Arcadian universe whenever I visit, and because you have supreme destiny power and Hanajima is too hot to lose. Also, my gospel of silver cannot be stopped by God or Man."
"Before a blazing fire he stood, cackling and triumphant as the Serpent wiggled in the flames behind him. Clad in a yellow jacket and pants, he held up a small doll hanging from a cord; she had dark hair and wore dark, gothic clothing. His eyes could be barely seen, but his mouth gaped open wide in a mask of arrogant triumph, and short black hair hung down on either side of his face. The mark of his father was upon him, but cut loose from all the things which normally held it back. It was the moment of his greatest victory, caught on cardstock for all to see. There had been few others to choose from, really."
Born in 1338, Nanbara was spawned by the summer rites which healed his father's deformities. Nanbara spent the first 20 years of his life being raised alternately at House Helgram and at the Amber Embassy (with his mother). He then walked the Logrus, and in 1358, his father assigned him to be the House Representative at the Black House, under the watchful eye of one of the Ten Swords. Nanbara took well in his own way to court life, and served in this capacity for 25 years, until 1383. During that time, he also studied law, and for the next decade travelled around the courts, studying their laws and practicing law himself.
An unfortunate encounter convinced him that he needed to strengthen his brain. Nanbara was suckered by a Marillith, who convinced him that his father and sister had been replaced by evil duplicates. This leads to the infamous 'Kanako the Doll' incident. Nanbara is saved from a suicidal attack on his father by Miroku, who manages to clean out his brain. Embarrassed and humiliated, Nanbara resigns from his post as Helgram's representative at the Black House, and plunges into his legal practice and seeks some way to strengthen his mind.
He sought out various instructors, and finally ended up being inducted into the Church of Serpentology, an obscure Serpent cult. Their techniques, designed to con people out of their money, in some ineffable way worked for him, perhaps because of him being a whackjob. He assisted the group with his legal skills, and spent the next fifteen years (1393-1408) practicing law and studying Serpentology.
In 1408, Lord Loewen told Nanbara he was going to have to go out into shadow and prove himself a warrior. Nanbara was eager to do so. Nanbara half-begs and half-browbeats Kurz, Melissa, Kaname, and Sousuke into helping him.
He spent two years gathering allies and training his forces, then rode out into shadow and swept down on the shadow of Chrysalin. Conquering it, he named it the Nanbara Empire. Then he settled down to rule it. He has since alternated between ruling it, getting into adventures with his generation, and making a pain of himself around the Courts and House Helgram.
Nanbara continues to be active in the Church of Serpentology, though he knows Loewen doesn't like it. In part, perhaps because of that.
Nanbara possesses his father and mother's strong sense of the rightness of their actions, magnified hugely and unjustified by reality. He also possesses a vast capacity for faith, combined with massive gullibility to anyone who plays on his ego.
He is a faithful, high-ranking member of the Cult of Serpentology, and loves to hint at his 'secret wisdom', though he never seems to raise the issue around his parents. From what you've been able to gather, the cult seems to blame everything bad on possession by Unicorn spirits (referred to as 'Rhoans' for no apparent reason), and is heavily into strange ritual exorcisms and the studying of the cult's books of lore.
Nanbara is a ranting egomaniac, but he's not actually malevolent towards people at random, though it's easy to become a target of his mostly impotent wrath. He has a great talent for finding loopholes and wiggling through them, which has made him a fairly effective lawyer.
Nanbara sees himself as a great lover. He is wrong, though he's not an entirely bad one, and he's had some success. Still, he overestimates his own attractiveness. He tends to take his sexual ethics from his father and House Helgram's attitudes. Love is to be a one-on-one thing, not a group thing like his mother's, although he doesn't seem to resent her for not marrying his father.
Nanbara is in some respects, more competent than he looks. He's mastered the basics of sorcery, and is as good a shifter and logrus user as most Chaosians ever become. His mind and body are of middling strength, and he can go three rounds with Miroku or Deirdre or Kanako and hold his own. These days, he's likely one of the best generals in the universe, and he's a fair hand with a sword as well.
Unfortunately, Nanbara is convinced he is the BEST, and anyone who beats him is, therefore, cheating. This makes dealing with him difficult.
Nanbara is known to carry a big-ass sword, given to him by Corey as a joke. It was not regarded with so much humor when he hacked the Marillith to death with it in a berserk frenzy after the doll incident.
Nanbara also rules over a medieval shadow empire about the size of the Mongol Empire, which, with his usual modesty, he has named the Nanbara Empire.
Nanbara is fighting hard against his engagement. And running around trying to help the family without getting killed. He's currently helping Sousuke out by conquering the G'ayoul.
Nanbara has also helped liberate Helgram from Abyssal invasion, and helped with the invasion of Lemuria too.
He has been made Suzuka's keeper.
He has since moved on to other things and achieved many victories and seems well on his way to becoming Loewen's favorite kid. Hard as that would have once been to imagine...