Azai Nagamasa makes a breif appearance in the anime. Even for the short time, you get a sence of what this character is like, devoted to his loving wife Oichi, the Azai Clan and justice.
Asai Nagamasa is husband to Oichi and brother in law to the Devil King, Oda Nobunaga. He loves Oichi deeply and for the sake of his wife's good name, Nagamasa turns a blind eye to the Oda clan atrocities, while in private he condemned his brother in law for his evil actions.
Nobunaga, however, knows that Nagamasa is not loyal to him as he is the one who arranged Oichi's marriage to the Azi clan. He sends the blood thirsty Mitsuhide off to eliminate Nagamasa while he was engaging Date Masamune in combat. (Sengoku BASARA Episode 5.)
Here he learns from Mitsuhide, when he lays bloody and dying in his lovers arms, that his marriage had been thus arranged for the destruction of his clan, and that Oichi had known about this.