Tomono debuted on the ISU Junior Grand Prix (JGP) series in August 2015, placing 13th in Riga, Latvia. He won the silver medal at the 2015–16 Japan Junior Championships and placed 16th at the senior men's competition. He was brought in to compete at the 2016 World Junior Championships in Debrecen, Hungary as a late alternate, after Sota Yamamoto withdrew. He qualified for the free skate in Hungary by placing 20th in the short program. His 12th place in the free skate lifted him to 15th overall.