The mysterious vetting process takes at least five years and is one of the Catholic Church's best kept secrets. But, somewhere in the Vatican's vast echoing halls and chambers, officials are believed to be close to ruling whether a Japanese warrior is a saint.

If confirmed, samurai Justo Takayama Ukon would become the first of Japan's feared fighters to achieve Christianity's greatest glory.

A romantic notion? Well, quite possibly it is, especially for a Samuri to not have some dark secrets – indeed, there are those in Japan who claim he was more sinner than saint.

Tokyo-based samurai expert Tamura Ryo said: "Takayama may have protected Christians but he was a killer too, motivated by self interest and by no means entirely a good man."

Those in favour of Takayama's elevation to sainthood vehemently disagree.

Takayama supporter Cardinal Thomas Maeda insists: "This brave man offered his life to Christ and should definitely be made a saint."

Before we consider the intrigue behind samurai Takayama's path to sainthood, his life history is well documented and broadly uncontested.

He was born around 1552 into a noble family during the tumultuous Sengoku period when Japan's countryside was ravaged almost continuously by wars and social unrest.

He was initially raised as a Buddhist. His conversion to Catholicism came at age 11 after a debate between his father and a Christian missionary led to their baptism.

Takayama and his father were responsible for the conversion of tens of thousands of Japanese and throughout his life, Takayama became a protector of Christians, using his influence to support missionary efforts despite facing severe persecution.

But, in 1587, chief imperial minister Toyotomi Hideyoshi ordered the expulsion of missionaries and demanded that Catholic feudal lords, like Takayama renounce their faith.

Twice Takayama refused to abandon his beliefs and for this he was stripped of his rank and authority.

He was exiled from Japan and fled with 300 other Christians to the Philippines, where he died in 1615 allegedly as a result of earlier ill treatment in his homeland.

It's said that in his last breath he called on his grandchildren to stand firm with their Catholic faith.

Supporters claim Takayama's legacy continues to inspire many as a symbol of unwavering faith and resilience in the face of adversity.

However, those who question his passage to sainthood point out there is undisputed evidence Tamayaka led raiding parties to smash Buddhist and Shinto shrines and temples.

Worse still: a high-ranking Japanese Catholic source, who asked not to be named, says:"Takayama definitely killed at least one person – not the actions of a saint."

Tamura Ryo, of the Tokyo Samurai Museum, has similar concerns, and claims Takayama was a mere opportunist hungry for power.