His early work were diverse in genre, but Yonezawa was struck when he read Kaoru Kitamura's Flying Horse (空飛ぶ馬) and Princess in Rokunomiya (六の宮の姫君) while in university, and decided to turn his attention to writing mysteries.
His decision to submit was fueled by positive reception of Hyōka on his website Hanmuden,[3] that he personally saw a future in the combination of light novels and mysteries,[6] and because he was late for the deadline of another award.
However, when Yonezawa had completed the draft for the third and what he intended to be the final book in the Classic Literature Club series, the label was going on hiatus due to changing trends in the market, so he could not get it published.
[7] Despite this, he was approached by Tokyo Sogensha who inquired what he was working on,[8] thanks partly to recommendations from writers Kiyoshi Kasai and Kazuki Sakuraba.
In the same year, he published Shunki Gentei Ichigo Taruto Jiken (春期限定いちごタルト事件), the first novel of the Shōshimin (小市民) series.
In 2008, when Yonezawa published Hakanai Hitsuji tachi no Shukuen (儚い羊たちの祝宴), he states that he started not only paying attention to the riddles present within his works, but also how they appeal to a wider audience.