Shirō was born in 1621 as the son of Catholic parents, Masuda Jinbei (益田 甚兵衛), a former Konishi clan retainer, and his wife.

Urban legend speculates that Shirō could have been the illegitimate son of Toyotomi Hideyori, but these claims have little credibility.

[citation needed] Portuguese Jesuit missionaries had been active in Japan since the late 16th century.

They mounted a coordinated defense that held off attackers, but the rebel force had no logistical support, and their resolve was weakened.

His head was displayed on a pike in Nagasaki for an extended period of time as a warning to potential Christian rebels.