For the first time Seika Aoyama made an international appearance at the World Youth Championships 2013 in Donetsk . There she reached the semi-finals over 200 meters and won the bronze medal with the Japanese sprint relay (1000 meters). In 2014, she reached fifth place over 400 meters at the Asian Games in Incheon, South Korea, and won the silver medal in the 4 x 400 meter relay. With this season she also took second place in the B final at the IAAF World Relays 2015 in the Bahamas . The Japanese also qualified for the World Championships in Beijing , but they were eliminated in the preliminary run despite a new national record. Two years later she finished seventh over 400 meters at the Asian Championships in Bhubaneswar and reached sixth place with the Japanese 4-by-100-meter relay and won the bronze medal with the 4-by-400-meter relay. At the Asian Championships in Doha in 2019 , she also won the bronze medal behind the teams from Bahrain and India in 3: 34.88 minutes. Then she came at the World Relays in Yokohama with the 4-by-400-meter relay in 3: 35.12 min in the B-final on the seventh place and was eliminated with the mixed relay in the preliminary run. At the end of September she took part in the mixed relay at the World Championships in Doha and was eliminated there with 3: 18.77 minutes in advance.
In 2016 and 2019, Aoyama became the Japanese champion in the 400-meter run.
Personal best
100 meters: 11.77 s (+0.3 m / s), October 18, 2014 in Nagasaki
200 meters: 23.78 s (−1.6 m / s), July 12, 2013 in Donetsk
400 meters: 52.85 s, September 2, 2016 in Kumagaya