In this article, I probe into the definition of banter duets, sio-po-kua, the form of sbuochang narrative singing, and its denomination. First I will discuss the general definition of banter songs, differentiating between researchers' interpretations and the possible idea koa-a booklets editors held of banter songs and banter duets. I then state the exact form of banter duet in koa-a booklets, which aside from the prefatory and concluding sections, invariably contain a body of duets. (Only a handful of koa-a booklets feature solos.) The titles of koa-a booklets and their contents are examined in five aspects to determine which count as banter duets. I conclude that editors or publishers of koa-a booklets may have other considerations when naming their titles. Therefore, we ought not determine the nature of the banter songs merely by way of its booklet title. A more precise and detailed classification will benefit the research of koa-a booklets.