Currently, webtoons, which appeared and developed with the spread of the Internet, are a representative type of cartoon in our nation. As a dominant form of webtoons, the vertical scroll canvas, which continues infinitely, has attracted much attention due to its distinctly different characteristic from that of published cartoons, leading to much related research. Therefore, a ‘page’ shown as a single image when scrolling is stopped while reading a webtoon and is regarded as insignificant, and it is even assumed there is no complete ‘page’. However, when reading a webtoon, the two main activities are scrolling down and stopping to look at the pictures and read the text. This study found that the image shown when a reader stops scrolling is similar to a page of a published cartoon, referring to such imagery as a ‘flexible page of a webtoon’. The research thus defines the unit of a webtoon and investigates how the elements that make up the page are framed. Subsequently, a case study of the webtoon "A Most Virtuous Villain" directed by the researcher based on the web novel “A Most Virtuous Villain” written by Lee Huin is used, with an explanation of how the flexible page of a webtoon is applied at the stage of production. We discuss how this flexible page generated when scrolling and reading webtoons is the conceptual unit necessary for the production, appreciation, and criticism of webtoons.