Actually, the idea probably first appeared in a game by Kitani Minoru, who tried it against Karigane Junichi in 1928, but in the very tiny handful of positions where it has been used before Yi, it has been very heavily influenced by the surrounding position. Yi seems to be the first to have used it in open field. However, this was not the first such occasion. He tried it (unsuccessfully) against An Tal-hun in the 9th Ch'eonweon on 18 October 2004.

This is how the opening developed in that game (Black facing komoku in lower right, lower left empty).