It is used to paint white cut lines that appear when printer paper is cut. Doing this painting will give your papercrafts a more beautiful finish. There is one point to note compared to markers. With pencils, you have to paint a little harder to get the color to stick. This can cause the paper to break accidentally or the surface to peel off.
Some types of printer paper have a coating that enriches surface colors. The color painted on these cut lines may be darker than surface colors. For this reason, it is recommended to use colors lighter than those colors.
This page introduces shuttle art products as an example. This is because they are inexpensive and come in a wide variety of colors. However, from checking the product reviews, this brand is likely to have defective products mixed in. Please be careful when purchasing. Please refer to the website links for detailed features and prices.

Website：Product page, Amazon
Brand：Shuttle Art