What a senior-debut breakthrough season this is for Yumeki Kojima, at 17, his first Asian Games title in a pantheon brimming with promise and bolstered by a 4:07.02 World junior record in the 400m medley in front of a home Tokyo crowd on day 3 of the continental showcase.

His victory turned tables on teammate Tomoyuki Matsushita, who topped the host's 1-2 punch in the 200IM on Sunday, the hosts also celebrating another top two finish as Matsushita stopped the clock in 4:09.64, the bronze a distant 4:14.59 from China's Wang Shun.

A quick recap on Kojima's stellar season: on 21 March 2026, he set a world junior record in the 200 IM in 1:56.53. Then, last month at the 2026 Pan Pacific Swimming Championships, he grabbed gold in the 200m backstroke in 1:55.38, and took down the World junior mark in the 400m medley heats in 4:08.69.

The follow-ups got faster still this week: 1:55.36 in the 200IM final for silver 0.06sec shy of Matsushita; now a 4:07.02-of-a-teenage-sledgehammer in a 400m final in which the Kojima trailed his quarry top half-way (Matsushita 54.95/1:03.54 vs Kojima's 56.16/1:04.25) before clawing 2sec back on breaststroke (1:09.72 vs 1:11.61) and then thundering ahead on freestyle (56.89 vs 59.54):

Medley times have changed with the advent of Léon Marchand, the French winner of four golds at a home Olympics in Paris two years ago. His world medley records stand at 1:52.69, 2025, and 4:02.50, 2023.

All of which highlights other teenage pathfinders in the 400IM:

• it was 1994 when 18-year-old Tom Dolan (USA) set the global 400m pace at 4:12.30WR for the World title in Rome
• it was 2002 when 17-year-old Michel Phelps rattled the pace of Dolan's first 400IM standard in 4:12.48. Before his 18th birthday, the budding GOAT changed the game like this: 4:11.09WR; 4:10.73WR.
• At 18, Phelps took the pace below 4:10 for the first time in history, on 4:09.09WR.
• At 19, Phelps lowered the mark to 4:08.41WR, then 4:08.26WR.
• There would be three more world marks to come, for a record eight pioneering swims before the biggest pantheon in Olympic sports history would be sealed: 4:06.22WR for the 2007 World title at the start of a campaign that in itself was a game-changer for a number of trend-setting reasons; 4:05.25WR at U.S. Olympic Trials in 2008; and 4:03.84WR for the first of an all-time, all-sports record eight golds at the Beijing 2008 Olympic Games.
• It was July 2023 when that 2008 record fell, to Marchand for the world title in Fukuoka. And there it stands as ...

One of the next targets for Kojima to chase. At a glance, this is how the balance of the virtual race of Marchand 2023 vs Phelps 2008 vs Kojima 2026 ebbs and flows, Marchand the marker, Phelps the fastest home comer yet, just ahead of ... Kojima this day 18 years on (and a glimpse, perhaps, of why we found Marchand practising a 3:43 400 free victory in Paris that ended with a 56.41 100 free split... the era of sub-4min 400IM is nigh...):

Léon Marchand Heralded By Michael Phelps After Magnificent 4:02.50 Takes GOAT’s Last World Record

As French sensation breaks the GOAT’s last solo World record, Michael Phelps says: “I’m just happy I have the longest-standing world record. I said to Bob [Bowman] earlier this year, ‘I think this kid has the potential to break four minutes’.”

State Of Swimming +Craig Lord

• Tokyo 20206 RESULTS IN FULL

Below:

• Peng Pioneers 1st Asian Sub-2:06
• Zhang Eyes Four-Gold Feast With 1500 Win
• Haughey repeats her 100-200 Free Double of 2023
• Li A Class Apart on 4:02 To Retain 400 Free Title
• China Hold Off Japan in men's 4x100 medley for Gold No15 in 3 days