In 1939 Funakoshi joined the Shin Seisaku Kyōkai (新制作協会, "association for new art") and helped to organize its sculpture division.

In the same year he converted to Catholicism and his new faith proved to have a profound influence on his work, which started to feature Christian motives.

From 1958 to 1962 he created the sculptures Twenty-six Martyrs of Japan and later the Hara-no-Jo (原の城, Christian samurai).

For the former sculpture he was awarded the Takamura Kōtarō Prize (高村光太郎賞受賞) and the pope bestowed the Order of St. Gregory the Great on him in 1964.

In 1987 he suffered a stroke, which forced him to switch to his left hand for his future art work.