In Tsuruya Namboku the fourth, who was famous for "Tokaido Yotsuya Kaidan", was a writer of Kabuki in the early 19th century which is called the "Kasei" era. The direction of my research was decided when I discovered a script Keiseiideno Yamabuki (1786 at Nakamura-za) which was written during his apprenticeship. Although the work was written by his mentor, Kanai Sansho, Namboku wrote one act of it. In those times, scripts were usually written by playwright teams. Sansho was a head of one of these teams and Namboku worked under him. Namboku has been studied a lot; however, there are not many researches in the aspect of the influence of his mentor.
I started my studies with clarifying the style of Kanai Sansho. Sansho is a little known writer today, because none of his works remained except one script. I unveiled Sansho's entire achievements by precisely analyzing this only script (On Ureshiku Zonjisoga, 1790 at Ichimura-za) along with examining thoroughly the descriptions of his work in a review book called Yakusha Hyobanki. Then, I used the results to analyze Tsuruya Namboku.
I found out that there were some similarities between the styles of Kanai Sansho and Tsuruya Namboku; such as exchanging the characters of hero and villain to trick the audience; dropping hints by using props cleverly to construct a complicated story; and using black humor, for example, treating homicide humorously. This meant that Namboku inherited the style of Sansho. I summarized the results and published a book Studies of Edo Kabuki Writers: From Kanai Sansho to Tsuruya Namboku (2012, Kasamashoin), which won the 6th Researcher's Award of Japanese Classical Literature.