F.F. - The Witness (F・F-目撃者 Efu Efu - Mokugekisha) is the sixteenth story arc in Stone Ocean.
It narrates Yo-Yo Ma's defeat and the fight between Foo Fighters and Pucci.
While Anasui has successfully neutralized Yo-Yo Ma by fusing his brain with that of a frog, Pucci celebrates the soon to be born Embryo, but sees that F.F. is planning to kill D an G.