Tsuka Sato, a graphic designer who appreciates the design direction of the main notebook itself. The "TS" series is the cover made from leather that was selected by the table every year. The 2019 edition is made with sheep leather for an elegant cover. Leather name "Bubble Sheep". It features a unique softness, and is fluffy and resilient to the touch. Unlike cowhide leather, it is also a precious leather that does not take up much space at once.