A composition includes first, second, and third components. The composition preferably includes 0.1 to 50 parts by mass of the third component with respect to 100 parts by mass in total of the first and second components. The first component is at least one type of melamine salt selected from the group consisting of melamine orthophosphate, melamine pyrophosphate, and melamine polyphosphate. The second component is at least one type of piperazine salt selected from the group consisting of piperazine orthophosphate, piperazine pyrophosphate, and piperazine polyphosphate. The third component is cyanuric acid or zinc cyanurate.