"Peripheral characters" refers to individuals in a story who are not the main focus or central to the plot. They play smaller roles and their presence usually helps to support or enhance the main characters and the overall story. Full definition
Not only does it allow for more character development, but it gives some of the more peripheral characters their chance to shine. (blog.bullz-eye.com)
These five central characters are all sharply written and well - acted, but the film's peripheral characters don't fare as well. (latimes.com)
Add to that fact that there are a number of peripheral characters written purely to conform to the traditional animation stereotypes and you have a significant amount of poor characterisation. (hoopla.nu)