The wife of Azai Nagamasa and sister of Oda Nobunaga. She is depicted as a slender woman who is very melancholic and depressed, always thinking that everything is her fault. She was at first sent by her brother, Oda Nobunaga, to marry Azai Nagamasa and spy on him. However, she genuinely fell in love with him and was torn between betraying her brother and her lover. While considered innocent looking, she also has a dark side which can become dangerous once she snaps. She wields a double bladed naginata, which she can separate and chain-link to its bar. In Sengoku BASARA 3/Anime, she fights only with her hands of darkness.
After witnessing her husband's death at the of hands of Nobunaga and then being forced to fight on in Nobunaga's name, she slowly started to lose her sanity. In the end, she succumbs to her own dark powers, which leads her to kill Nobunaga's retainers (Nōhime and Ranmaru) and eventually Nobunaga himself. After killing her brother in Honnō-ji, Oichi regains her sanity for a little while, then breaks down in tears at her atrocity to her family and clan. The temple collapses and she's presumed dead afterwards. She's often considered as the most tragic character of Sengoku Basara.
Oichi inexplicably returned in Sengoku Basara 3 having lost her memories after suppressing the pain of witnessing Nagamasa's death and being forced to do cruelties under Nobunaga's name in the past. Rather than bearing the Azai crest, she now uses the Oda crest. In her Red route, she joins Ieyasu - Lord Happy - because he's nice to her and wants to always be there for her, and fights for him, despite his asking her to stay behind. She chooses to kill Mitsunari - Lord Grumpy - to save him from the "hole in his heart". In her Green route, she follows a voice, leading to a battle with either Tenkai or Kobayakawa. Fighting Tenkai makes him admit that he lured Oichi to him, with the desire to ressurect Nobunaga. This transfers her to the Purple Route, where Tenkai is killed by Nobunaga, and Oichi then defeats the repeatedly resurrecting Nobunaga, capturing him, and dragging them both down to the depths of hell, claiming it to be the purpose she now lives for.