Japanese swim star Daiya Seto has set his sights on claiming one of Michael Phelps' world records at the upcoming Tokyo Games, after winning at his country's Olympic trials on Saturday.

Seto finished the 400-metre individual medley in four minutes and 9.02 seconds at the Japanese national championships, held at the venue where the swimming events will be hosted this summer.

Seto's time was well short of Phelps' world benchmark of 4:03.84 -- which has stood since the 2008 Beijing Games -- but he is aiming to overhaul it when he hits his peak this summer.

"I'm aiming for the world record, but I want to get at least 4:04 at the Olympics," said Seto. "To get my time tonight with my body in the condition it's in, I feel like I'm working towards the gold medal."

While the nationals also double as Japan's Olympic trials, Seto had already secured his 400 IM spot at the coronavirus-postponed Games after winning the world title in 2019. Seto will be joined by Yuki Ikari, who finished second in a time of 4:11.88. Seto returned to competition in February after being suspended from October to the end of last year for having an extramarital affair.

After being caught on camera with his girlfriend, he was banned from competitions and official training. He also quit as captain of Japan's team and was dropped by a sponsor.  But the 26-year-old is looking to build up a head of steam at this week's trials, where he will also compete in the 200 IM and the 200m butterfly.

Seto's compatriot Kosuke Hagino will not defend his 400 IM Olympic title in Tokyo, after opting to focus on the 200 IM. "I didn't have any pressure," said Seto. "I had already qualified but I wasn't thinking about that at all. I was thinking about what kind of performance I want to give in the summer."

Fellow star Rikako Ikee also has a chance at making Japan's Olympic team after she reached the final of the women's 100m butterfly. Ikee, who received a leukaemia diagnosis in February 2019, has played down her chances of appearing at the Tokyo Games. But her time of 58.48 seconds was the third-fastest of the semifinals.

The top two finishers from each final will make the Olympic team if they meet the qualifying standard time. Yui Ohashi won the women's 400 IM final in a time of 4:35.14, booking her Olympic ticket along with high school student Ageha Tanigawa, who clocked 4:37.90. "I've always wanted to be an Olympic athlete, so I'm just really happy about it," said Ohashi.

In the day's other final, Ryo Nakajima won the men's 400m freestyle in a time of 3:47.00, but fell short of the Olympic qualification mark of 3:46.34.