The piece began when I received a commission from the Tuba-saders with the concept of “an image of the city at night.” From the starting point of “Well, what should I do with that?”, the process of composing began. When I looked into what kind of music others had written on the theme of “the city at night,” I found that most of them (mainly Vocaloid songs) used the **Marusa progression**.
The Marusa progression refers to the chord progression used in Ringo Sheena’s song *Marunouchi Sadistic*. It’s a very emotional progression that evokes images of nighttime cities, highways, and illuminated skylines. Building the piece around this progression resulted in a tuba quartet that feels quite close to a pop song. Adding the optional caj?n part enhances the pop flavor even more.
The title was created by gradually transforming “Tuba-ssadors” → “Chuba-saders” → “Tsuba-saders.” This idea had actually existed since their previous commission, *Dr. Jekyll and Mr. Hyde*. I had thought, “Next time, I’ll use this concept,” and fortunately, I was given the opportunity to realize it sooner than expected.