Kunii becomes the next in a long line of riders to graduate from the Idemitsu Asia Talent Cup into the World Championship. He competed in the 2016 and 2017 editions and ended up sixth and fifth in the standings. 2017 also saw the Japanese rider embark on his full year in the Junior World Championship but it was in 2018 that he took his FIM CEV Repsol first victory. That same year, the Japanese rider also made his debut in the Red Bull Rookies Cup, with the highlight undoubtedly a victory in Mugello. Championship success in both series were the target for 2019 but injuries throughout the year made that dream unacheivable. However, he again took victories in both Championships and was rewarded with a Moto3™ World Championship seat with Honda Team Asia for 2020. A frustrating rookie season saw Kunii unable to bag his first World Championship point and will be hoping to rectify that early in 2021.