One of the theories is that Kukai burnt a Goma (holy fire) in the shape of the letter 'Dai (big),' which represents human body to drive plague off ("Topography of Yoshufushi" and "Hinami-kiji" (a guidebook of annual events in Kyoto and its surrounding area).
空海が、疫病退散のため、人体を表す「大」の字を書き護摩をたいた（『雍州府志』・『日次紀事（ひなみきじ）』）。