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.