Throne of Blood

Kurosawa's take on Macbeth: Miki and Washizu are sammurai commanders under a local lord who reigns in the castle in the Spider Web Forest. After defeating the lord's enemies in battle, they return to the lord's castle. On their way through the forest surrounding the castle, they get lost and meet a spirit, who foretells their future. The spirit tells them that today Washizu will be named master of the North Castle and Miki will now command Fort One. She then foretells that Washizu will eventually become Lord of Forest Castle, and finally she tells Miki that his son will also become lord of the castle.As the two return to their lord's estate, the lord promptly rewards the two with exactly what the spirit had predicted. As Washizu discusses this with his wife Asaji, she manipulates him into making the second part of the prophecy come true by killing the lord. When the lord visits, Washizu kills him with the help of his wife who poisons the lord's guards. When Washizu returns in shock at his deed, Asaji grabs the bloody sword and puts it in the hands of one of the three unconscious guards. She then yells "murder" through the courtyard, and Washizu slays the guard before he has a chance to plead his innocence.The lord's vengeful son Kunimaru and a rival of Washizu named Noriyasu both suspect Washizu as the murderrous traitor and try to warn Miki, who refuses to believe what they are saying about his friend. Washizu, though, is unsure of Miki's loyalty, but he desires to trust his friend and he still plans to let Miki's son be his heir, since he and Asaji have been unable to bear a child of their own.Washizu plans to tell Miki and his son about his decision at a grand banquet, but Asaji tells him that she is pregnant, which leaves him with a quandary concerning his heir. During the banquet, Washizu is distrurbed that his friend and his son have yet to show up. He then begins to panic at the sight of Miki's ghost, and Asaji tells their guest that he is drunk and that they leave. Then one of his men arrived with the severed head of Miki, and Washizu realizes what his wife has done behind his back. The guard also tells them that Miki's son escaped.Later, distraught upon hearing of his wife's miscarriage and in dire need of help with the impending battle with his foes, he returns to the forest to summon the spirit. She tells him that he will not be defeated unless the forest begins to move toward the castle. Washizu believes this is impossible and is confident of his victory. He returns to the castle to await the oncoming armies. Overnight the castle hears the sound of trees being cut down, though nobody can see it in the darkness. As Washizu rouses his attendants with encouraging words, birds start to flock the castle, which Washizu believes to be a good omen. He sits and waits, armed. After having nodded off, he is awoken on a dense and foggy morning by the screams of his wife's attendants, and he finds his wife in a semi-catatonic state, trying to clean the imaginary blood from her hands, obviously distraught at her grave misdeeds.Washizu knows he must kill all his enemies, so he tells his troops of the last prophecy, and they share his confidence. But when his troops notice the enemy approaching the castle hiding behind tree boughs, they see that the prophecy came true and that Washizu was doomed.As Washizu tries to get his troops to attack, they remain still. Finally they turn on their master and begin firing arrows at him as revenge for his traitorous actions. Washizu finally succumbs to his wounds just as his enemies approach the castle gates.

Question: Who does Washizu plan to name as his heir?
Answer: Miki's son