Upon graduating from Waseda University's school of literature, he took a position as a teacher of world history at a high school. After this, Yoshino joined the staff of Tokuma Shoten's Animage magazine as a writer. It was here that the Sunrise producer Naotake Furusato offered him a position in the studio as screenwriter.

Since joining Sunrise, the first series in which he was head writer and wrote the series composition was Mai-HiME, whose follow-ups Mai-Otome and Mai-Otome Zwei he has also gone on to supervise. He has also authored the manga adaptation of Mai-Otome (along with HIGUCHI Tatsuhito) and gone on to write numerous other manga series. He also the writer of Code Geass: Lelouch of the Rebellion and Gundam Seed.