This is an item of stationery (paper or writing goods), or other small merchandise such as good-luck charms, mascot straps, et cetera.
One box consists of 12 packs with each pack containing one randomly inserted mini clear drip mat. Each drip mat is in B6 size (12.8 x 18.2cm) and feature one of sixteen possible illustrations of various characters from the "D.C.II" series as shown in the picture below.