Hyouka
The mystery genre of Anime and Manga was dull (or boring) until the Manga and Anime adaptation started airing. The whole plot of Hyouka revolves around a high-school (grade 9 - 12) boy, Ho(u)taro Oreki, who solves multiple mysteries without even him noticing (except some parts where he does). The basic concept of Hyouka was very simple (or plain) at the time it was airing. In fact, it was too simple that many people thought it just a regular mystery anime or manga. However, as simple as the concept is, the build-up is very mesmerizing (or fascinating), to say the least. Fans who were interested or not interested in mystery were mesmerized by the build-up of the riddles (or mysteries), that take place in the anime or manga.