A poised and mysterious highborn woman, Mariko is deeply faithful and darkly determined. She is married to Toda Hirokatsu "Buntaro" , more in duty than in love, and is a devoted Christian.
Highly educated and fiercely loyal, she is trusted by her lord, Toranaga. In Osaka , when the son of Lady Mariko's dear friend Fuji is sentenced to death after a mistake made by Fuji's husband Tadayoshi , she goes to comfort Fuji and calm her down as she hands her son over. Later, she plays a pivotal role in interpreting the encounter between Lord Toranaga and the English Protestant, John Blackthorne.
Mariko's honesty in translating Blackthorne's words and her insightful observations contribute to Toranaga's understanding of the situation. That evening, Lord Toranaga calls Mariko back for a meeting and asks her her thoughts about the encounter with the barbarian. She said the translations were honest and that her instinct is to guard against him. Hiromatsu asks Toranaga why even keep the barbarian around when his impeachment and possible death is on the line.
Mariko explains that he intends to sow division amongst the regents as he believes the Christian lords will disagree with Ishido. Buntaro comes in and tells Mariko that they, with John, will go to Ajiro. Yabushige , Nagakado and a group gather to set off to Ajiro with John, Kiri-no-kata , Mariko and others - without Toranaga.
When no one is looking, Mariko and John see Lord Toranaga discreetly go into one of the carriages, disguised, switching places with Kiri. Ishido leaves and wishes them a safe journey. His men escort them to the gate of the castle. En route, Mariko informs John that Toranaga is known for his trickery and that if he is found not only will Toranaga be killed but all of them will be. When exiting the castle gate, a man demands to verify every person leaving on orders from Lord Ishido.
