Nasukawa's father threw in the towel after 140 seconds of the first round on Monday as his 20-year-old son bravely teetered around the ring trying to get up.
With the Japanese fighter clearly battling to stay on his feet, the trainer rushed in and stopped the fight with less than one minute of the first round remaining.
Maybe just facing the legendary Mayweather, who went 50-0 before "retiring" again in 2017, is enough of a rub for Nasukawa to be seen as a potential superstar in the eyes of the millions watching on television in Japan.
Mayweather's second biggest earner came two years earlier when he outpointed Manny Pacquiao in a fight five years in the making.
Nasukawa was left in tears after the bout while Mayweather looked in good spirits having showboated for the entirety of the fight.
However, the same can't be said when it comes to the pre-fight build-up, where Mayweather caused controversy by arriving incredibly late to the Saitama Super Arena.
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United States boxing legend Floyd Mayweather Jr (R) smiles during an exhibition match against Japanese kickboxer Tenshin Nasukawa at the Saitama Super Arena in Saitama on December 31, 2018. "I'm still undefeated. This is just entertainment for the people", he added.
He wrote on Instagram: "I am disappointed at myself since I thought I could have done better".
It was announced out of the blue on November 5, with Mayweather saying it had "always been a goal of mine to go outside out of the U.S. and display my talent".
No rule set had yet been announced, with "Money" claiming Rizin had gone back on their original agreement for a three-round exhibition.
The fight began after a lengthy wait for Mayweather to emerge at the arena, which led many to wonder if he would show up at all, given the uncertainty over the event.
The event - hosted in Tokyo - was heavily criticised in the build-up and the bout itself proved far more one-sided than many had predicted, even if victory for Mayweather was nearly guaranteed.