Miyahara became eligible for junior international competition in the 2011–2012 season. She won a silver medal at her Junior Grand Prix debut in Gdańsk, Poland, and finished fifth at her second event in Milan, Italy. Miyahara then won the Japan junior title and placed sixth on the senior level. She was fourth at her first World Junior Championships. Miyahara was invited to skate in the gala at the 2012 World Team Trophy as the Japanese junior national champion.