Nobunaga Asakura is Yūto Ayase's childhood friend, attending the same private Hakujō Academy in the class next door. He possesses a cheerful and openhearted personality and achieves excellent academic grades, widely recognized as a bishōnen by the female student body. Despite his popularity and attractive appearance, he remains single due to his open, passionate involvement in otaku culture. A hardcore otaku, he possesses extensive familiarity with Akihabara's layout and establishments, where he holds significant recognition. His high volume of purchases at Animate earned him the nickname "Kaiser" and one of only three golden Animate cards in existence. A framed gold picture of him shaking hands with the manager hangs prominently at the "@Home ~Café" – where Haruka Nogizaka once worked part-time – bearing the caption "Welcome home, our greatest master".

He belongs to the historical Asakura clan, which sought to dominate Japan during the Sengoku period, creating irony in his name as it references Oda Nobunaga, the daimyo of Owari and a key adversary of the Asakura clan during Japan's unification. He has a younger sister, Mahiro Asakura, who views him as an "idiot older brother", dislikes his otaku hobbies, and harbors affection for Yūto. Mahiro does not appear in the anime adaptations.

Throughout the series, Nobunaga maintains a supportive role as Yūto's confidant. Aware of Yūto and Haruka's relationship early on, he occasionally teases Yūto about it without negative interference. His otaku expertise frequently surfaces, such as attempting to involve Yūto in anime and manga culture, including late-night calls to discuss television shows. He becomes particularly enthused when Yūto's association with Haruka leads to more frequent Akihabara visits, interpreting it as a potential shift in Yūto's interests. His reliability and energetic personality make him a steadfast friend, evident during incidents like the threat to Haruka's secret, where he implicitly backs Yūto's efforts to protect her.

His character remains consistent across all media, including the main series, the second season *Purezza*, and the OVA *Finale*. He appears alongside Yūto and their teacher Yukari Kamishiro in cameo roles within the manga series *Kyōhaku Dog's*, another work by the illustrator Shaa, indicating a shared narrative universe.