The scroll is used to extend the impression of time and place of the scenery that the display is showing. In a more or less implied way. Specially at the shohin style Toko-kazari display the scroll is always used.The motives of the drawing or painting will almost always be aimed at nature. In a private Tokonoma display that is more personal other themes of a more philosophic character may be shown.
The main role of the scroll is to elongate the impression of nature, underlining a certain feeling and even with a philosophic approach. It can be reflected by calligraphy, a bird flying i.e. but newer repeating what`s in the Tokonoma display. Do not use a painting/scroll showing branches of a tree, when branches are already presented by the bonsai. Use such a picture with a Suiseki instead. Also flowers at the scroll painting is not used when setting up a flowering bonsai, because it is a repetition of the theme.