Japanese flat image of a Christian symbol, usually the crucifixion, designed to be stepped on. Suspected Christians were required to step on the representation of Jesus or the Virgin Mary to prove that they were not believers. At one point in Japan, Christians were persecuted by the Shogunate, because the Japanese feared that the influence of Christianity would make Japan too westernized. To be a Shintoist was to be loyal to Japan.
Fumi komi means crushing in Japanese. When someone gets crushed (Stepping on someone's foot, embarrasing someone, roasting someone,...) you yell fumi komi.
When Dave roastedBob in a rap battle everyone yelled: "Fumi Komi!"