The 26-year-old Kerevi, the Wallabies vice-captain, had a superb season. He was the runner up to fellow Fijian Marika Koroibete as the Wallabies' player of the year, but Kerevi was often their most damaging runner.
The Reds centre was also Australia's Super Rugby player of the year, but RA lost a bidding war with the Japanese club for his services.
"My manager has told me to go to Japan so that I can aim to play for Fiji in the next Rugby World Cup," the Fijian paper reported Kerevi as saying.
"It (is) all in the air for me to focus on Japan.
"I cannot play for the Wallabies because I cannot reach the threshold of 60 caps, which they are trying to lower."
Former All Black Charles Piutau, who wanted to play for Tonga at the World Cup, is among the notable players who have investigated switching nations.
So long as players have the relevant passport, they can switch via a three-year stand down and then playing in an Olympic sevens qualifying tournament. Piutau missed out on the 2019 World Cup because Tonga ran out of qualifying tournaments to play him in.