Ikkō Irino, also known as Kazuteru Irino (納野 一光), is the deceased grandfather of Nagomu Irino and father of Heigo Irino. He belonged to the Irino family lineage that owns and operates the traditional Japanese confectionery shop Ryokushō in Kyoto. His given name Kazuteru merges the characters for "one" (一) and "light" (光), while the surname Irino signifies "settlement, obtain" (納) and "field, wilderness" (野). As a former member of the family business, his legacy shapes Ryokushō's current operations and succession considerations, particularly influencing future leadership decisions involving Nagomu and Itsuka Yukihira. His absence resonates within the family dynamics.