The blue hour — that fleeting period just before sunrise when the sun lingers below the horizon, its scattered light painting the sky in deep cobalt — is 24-year-old Chinese swimmer Sun Jiajun's favorite time of day.

That transitional magic, where darkness gives way to dawn, mirrors the defining moment of his career: the men's 4x100m medley relay final at the Paris Olympics last August.

Originally a backup, Sun earned his spot in the men's medley relay after outperforming teammate Wang Changhao — who clocked 52.37 seconds in the 100m butterfly — with a time of 51.85 seconds three days earlier, as Wang battled fever-induced fatigue.

As the relay's third leg, Sun even skipped breaths in the final stretch to unleash a personal-best 51.19-second butterfly split.

"I told myself to go all out, to fight like there was no tomorrow. I had to gain more time for the fourth leg, Pan Zhanle," Sun recalled.

In the end, the quartet — backstroker Xu Jiayu, breaststroke world champion Qin Haiyang, Sun, and freestyle anchor Pan — shattered Team USA's 64-year Olympic dominance in the event, clinching gold.

That "no-holds-barred" sprint became Sun's professional blue hour: a twilight threshold between promise and breakthrough. The Paris crucible forged a new mindset — now, he focuses on "perfecting the process".

"I don't know what's ahead, but I'll focus on giving my best to today's training and rehab. The future is uncertain, but today is mine to control," said Sun.

This mindset shift proved transformative. Just one month after the Paris Olympics, Sun dominated at the 2024 National Swimming Championships in Wuhan, claiming gold in both the men's 50m butterfly and 50m breaststroke events.

ALSO READ: A relay impressive haul

Yet his journey wasn't without struggles. Before that Paris final, Sun battled severe anxiety. "The pressure was overwhelming. I couldn't sleep at all, which made me even more worried, because poor rest affects performance," he recalled.

Olympic champion Wang Shun, his roommate at the time, became his solace. "He noticed my anxiety and shared his own experience," Sun recalled.

"He told me that, before the Tokyo 2020 200m individual medley final, he couldn't sleep either — yet he still won gold the next day. His story showed me that even champions face these moments, and that the challenge is surmountable."

To mark Youth Day, which fell on May 4, Sun offered one piece of advice, which carries some hard-won wisdom, to aspiring young athletes: "The future matters less than your commitment to the path you choose. Stay steadfast, and success will follow."

Born and raised in Yichang, Hubei province, Sun Jiajun grew up under the care of his grandmother.

In 2006, when he was just six years old, his grandmother first sent him to a summer camp where he was introduced to swimming. He was soon selected by a coach to join the city's sports school for systematic training. In 2013, Sun was chosen to join the Hubei Provincial Swimming Team.

Zheng Shan, his coach at the time, recalled: "When Sun first joined my training group at about 12 years old, he was very mature for his age and exceptionally hardworking. His greatest qualities were his passion for both swimming and life, and his unwavering dedication once he set a goal. He never cut corners in training — in fact, he often asked to increase the intensity and workload."

Five years later, Sun earned his place on the national team.

When asked about life outside the pool, Sun shared his love for movies — especially suspense and detective films. He dreams of coastal getaways, mentioning Sanya in Hainan province as a perfect retreat.

Looking further afield, his travel bucket list includes countries in Europe's far north, like Norway and Iceland.

READ MORE: China wins men's 4x100m medley relay gold at Paris Games

"I'd love to experience the blue hour there," he said.

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FACTFILE

Name: Sun Jiajun

Age: 24

Birthplace: Yichang, Wuhan province

Event: Swimming

Hobbies: Watching movies; building LEGO

Career Highlights:

2024 Paris Olympics:

— Men's 4X100m medley relay gold

2024 National Swimming Championships:

— Men's 50m butterfly gold

— Men's 50m breaststroke gold