Self-described "rowdy character" Tomoru Honda kept his cool to clinch a place in Japan's Tokyo Olympics swimming team on Tuesday, qualifying alongside star Daiya Seto in the 200-metre butterfly.

Honda, who confessed after the race that he "just can't calm down" in his daily life, put in a late surge to finish ahead of world silver medallist Seto in a time of 1 min, 54.88 sec at Japan's Olympic trials.

Seto also booked his spot in a third event at the coronavirus-delayed Games with a time of 1:55.20.

But it was Honda who took centre stage, heeding his coach's advice to keep a clear head even when Seto streaked off into the distance early on in the race.

"I'm a rowdy character, and I'm always being told to stay cool," said Honda, who will be making his Olympic debut.

"My coach has been telling me since I was in junior high school that if I don't stay calm in a race, whether I'm feeling down or feeling happy, I'll wear myself out. It's something that I've always tried to keep in mind."

Seto had already qualified for the Olympic 200m and 400m individual medley going into the trials, by virtue of his 2019 world championship wins in both events.

But he has yet to hit his peak this year after serving a suspension for having an extramarital affair.

Seto returned to racing in February after being banned from competitions and official training from October to the end of last year.

He also quit as captain of Japan's team and was dropped by a sponsor in the wake of the scandal.

Tomoru Honda kept his cool to clinch a place in Japan's Tokyo Olympics swimming team
Tomoru Honda kept his cool to clinch a place in Japan's Tokyo Olympics swimming team AFP / CHARLY TRIBALLEAU

He started this week's trials by comfortably winning the 400 IM and setting his sights on claiming Michael Phelps' world record in the event this summer.

But he acknowledged he still has work to do after losing to Honda in the 200m butterfly.

"I need more training, and with that I can definitely win gold," said Seto.

"My main event is the 400 IM, and I'm aiming for the world record in that. If I can get near Phelps' record, then I can get near the gold medal in the 200 butterfly and the 200 IM. I want to train with that in mind."

Elsewhere at the Japanese trials, Miho Teramura and Yui Ohashi both clinched Olympic berths in the women's 200 IM.

Teramura finished first in a time of 2:09.55, ahead of Ohashi in 2:09.67.

Ohashi had already booked her place in the Olympic 400 IM earlier in the week, but she had to grit her teeth to clinch the double.

"I did what I set out to do in the first half of the race, but then my body seized up after the 100m turn and I thought 'uh oh, I'm in trouble here'," she said.

"I just managed to clinch my place at the last, but I need to think a bit more about my training."

Chihiro Igarashi won the women's 200m freestyle in a time of 1:57.47, but it was not enough to meet the qualifying time for the individual event.