After Blackthorne was serious injured in an attack that killed his lover Mariko Lord Ishido requested that someone from the Jesuit order escort the injured Blackthorne back to the Japanese galley that would take them back to Anjiro and his ship the Erasmus. Brother Michael was sent to perform this duty. On the way back they stopped at the Jesuit mission in Osaka as Father Dell'Aqua wanted to personally ensure Blackthorne's safe passage to the galley.
Blackthorne and his escorts were forced to pass the Black Ship - the Portuguese treasure ship - in order to reach the galley. Captain Ferriera wanted Blackthorne dead and was past the point of caring whether or not he got excommunicated for the act. Brother Michael observed the deteriorating situation and when Ferriera raised his pistol to shoot Blackthorne Brother Michael had the Christian samurai escorting them put a bunch of arrows in the Captain's chest, ending his life.
After explaining that it was his duty to protect Father Dell'Aqua, the priest forgave Michael for his actions.
Brother Michael was loosely based on Chijiwa Seizaemon. He was baptised as Miguel in 1580, and traveled to Europe as an envoy from the Christian daimyo Omura Sumitada in the 1580s. After the anti-Christian edicts of Toyotomi Hideyoshi were passed in the 1590s he returned to Japan. Little is known of his later life but his tombstone was discovered in 2004 in the town of Tarami, Nagasaki Prefecture. 
In the television miniseries he was one of only three Japanese characters who spoke English, the other two being Mariko and Urano.