Silent Sprint is a power-up for Sly Cooper in 40 Thieves in Sly Cooper: Thieves in Time. It costs 1000 coins and is available after completing "Open Sesame." Rioichi Cooper has this as a default ability.
This power-up allows Sly and Rioichi to sprint (holding while moving) without alerting any guards. This also adds a motion blur effect to the sprint animation.
Given his profession, Rioichi most likely learned the Silent Sprint during his ninja training. However, as with the Leaping Dragon Technique, Rioichi did not write the technique in the Thievius Raccoonus.