Weak rules over eligibility to play for a country is one of the characteristics of rugby, and the Japan team is no exception in capitalizing on the benefits of it in seeking to reach the knockout stage for the first time at the ongoing World Cup.

A record-high 16 foreign-born players have been selected in Jamie Joseph's 31-man squad for Japan, captained by New Zealand-born Michael Leitch for the second straight time.

Kotaro Matsushima and Pieter Labuschagne, born in South Africa, combined to score four tries in Japan's 30-10 win over Russia in the World Cup's opening match on Friday.

Foreign-born players have played for Japan since the first World Cup took place in 1987. New Zealander Joseph, who played for Japan in the 1999 World Cup, has said they help make up for the physicality the Japanese players lack.

But the diversified team has not always been welcomed in the country, especially when Japan failed to deliver results. When the Brave Blossoms finished winless with a draw and three defeats at the 2011 World Cup, the team's dependence on foreign-born players was questioned in some circles.

Ahead of the 2015 World Cup, Leitch said he had second thoughts about captaining because he was foreign-born, while New Zealand's Luke Thompson also said he was hurt by the criticism of there being too many foreign-born players on the squad.

But when Japan, amid low expectations, achieved a historic three-win run at the previous World Cup in England in 2015, the contributions of the foreign-born players drew renewed attention.

Star fullback Ayumu Goromaru wrote on Twitter shortly after Japan's famous win over South Africa, "Let the spotlight shine on foreign-born players on the Japan team especially now when it is gaining attention."

"They are the best teammates who have made a choice to compete for Japan rather than their home country," he wrote.

Leitch, born in New Zealand from a Fijian mother, has become a symbol of diversity for the Japan team since coming to Hokkaido at age 15 and later joining Top League side Toshiba Brave Lupus.

He has said he made a choice to play for Japan as a "way to repay for the kindness" in making him one of Japanese rugby's competitive players.

"The three years at Sapporo have laid the foundation, and I could go to the World Cup because of hard work at Tokai (University)," said Leitch, who only weighed 75 kg when he first came to Japan, surprising the coaches at his high school.

Among other foreign-born players for the Brave Blossoms, Lomano Lava Lemeki, born in New Zealand to Tongan parents, turned pro in Japan in 2009 and also became part of the country's Rugby Sevens squad at the Rio Olympics in 2016.

South Korean-born Koo Ji-won attended Nihon Bunri High School in Oita Prefecture and Takushoku University, while Timothy Lafaele, from Samoa, spent time at Yamanashi Gakuin University.

The Japan team seeks unity by using the word "glocal," a mix of global and local. Foreign-born players are asked to introduce their mother countries to teammates while being taught to sing the Japanese national anthem by domestic-born players.

Regarding "Kimigayo," the national anthem, Pretoria-born flanker Labuschagne, who became eligible to play for Japan in June, said, "It's about how small stones become one big rock and in a sense that is what we are doing on the field, 23 different men all working together for the same goal."

A World Rugby regulation states that a player can represent a country by meeting one of four requirements — being born in the country, having one parent or grandparent born in the country, cumulative residency in the country for 10 years or living in the country for three straight years before playing.

The last rule was adjusted in 2017 to increase the residency requirement from three to five years, effective Dec. 31, 2020, to "ensure a close, credible and established link between a union and players, which is good for rugby and good for fans," according to World Rugby.

Tsuyoshi Matsushima, an associate professor at Ritsumeikan University, explains that the rule promoting internationality in rugby is the sport's "unique legacy."

He says that the current form of regulation, involving the residency record, dates back to the 1890s when in the United Kingdom — home to the rugby unions of England, Ireland, Scotland and Wales — the issue of eligibility of players was raised with many players hailing from its colonies.

"People may have awkwardness about foreign names and players who don't look like Japanese being on the Japan team, but rugby is a sport where players with various roots and physical characteristics respect each other and become united for a win," Matsushima said.