"Ninja Gaiden" was Itagaki's effort to develop a game centered on violent gameplay, with super ninja Ryu Hayabusa as the protagonist. Capitalizing on the brand name of the earlier NES series, Itagaki developed a critically acclaimed action-adventure game for the Xbox which also had an international online tournament held for it. He continued work on it to release "Ninja Gaiden Black" as the opus of his "Ninja Gaiden" work. He continued the series on the Nintendo DS with "", partly due to a promise made to his daughter. At the same time, he brought the series' next chapter onto the Xbox 360 as "Ninja Gaiden II".