Takao Osugi is the father of Suzuno Osugi, the Priestess of Byakko.
In Fushigi Yuugi Genbu Kaiden, Takao is a handsome young man who is a good friend of the Okuda family and has great respect for Einosuke, his mentor, as a scholar. He has known Takiko ever since she was a little girl, and she was in love with him but he was oblivious to it. When Takiko blurted out her feelings, Takao was sincerely stunned.
He's happily married to Tamayo Osugi and by the time Genbu Kaiden takes place, their daughter Suzuno is already eight years old and greatly admires Takiko, whom she sees as a big sister figure.
In Fushigi Yuugi: Byakko Senki, set few months after the end of Genbu Kaiden, Takao is the owner of the Universe of the Four Gods, which Einosuke entrusted him with in his last will. He tried to destroy it so no more tragedies like that of the Okuda family will happen (and to protect Suzuno and other women from being potential Priestesses), but all the methods he used (using an industrial kiln, sealing it in a Shinto shrine, etc.) have failed spectacularly due to the book's own magic. He and Tamayo are also deeply worried and burdened by what they know about the Book and the true reason behind the deaths of Takiko and Einosuke.
When Takao is getting ready to throw the Universe into the ocean or bury it in the mountains, the Great Kanto Earthquake of 1923 takes place and destroys Tokyo. Tamayo is fatally crushed by the debris of the Osugi home and Takao is severely injured, but Suzuno is unharmed thanks to the Book itself and its powers. Realizing that Suzuno will be safer inside the Book than in Tokyo, Takao uses his last minutes of life to send Suzuno inside it for her own protection, telling his daughter about Takiko's adventures inside it and reassuring her about his and Tamayo's love for her.