Toshiro Mifune did not receive an Oscar nomination for portraying Kikuchiyo in Seven Samurai.
In the group of the Seven Samurai there is the wise old leader, his young protege, a learned right hand man, a world weary veteran samurai, a poorly skilled but jovial samurai, a stone faced and most skilled of all of them, and Kikuchiyo portrayed by Mifune who is not even a samurai. Kikuchiyo in fact does not seem to really have a name, or at least either does not remember it or does not wish to state what it is. The other samurai in fact give him the name of Kikuchiyo which is in fact rather derogatory. Not really being a samurai he never really is just part of the group as some of the others are and Mifune's performance sticks out the most within the film.
Mifune early on in the film is off to the side as Kikuchiyo tries to join the samurai on their adventure even though all he has is a one huge sword, and a fake birth certificate to prove his worth. Mifune is terrific in just being a crazy man easy to being drunk, but very much a wannabe Samurai. Although at this point you cannot tell really where he came from but Mifune still is able to convey that his craziness comes from something in his history. Mufine is also great in just creating the dynamic between the insane Kikuchiyo he does anything but stand still against the rest of the Samurai who are all very stoic and reserved.
Eventually Kikuchiyo makes his way with the Samurai by basically just following them until they give in to allowing him to come as well even though his birth certification does very little to prove that he is of noble birth. He nevertheless becomes one of the most motivated of the fighters, even if his insanity never does seem to leave him. Mifune is like a wild animal at times, a particularly vicious one, as he shows the degree of passion Kikuchiyo does have in the fight. It is extreme and the most intense of any of the men hinting that Kikuchiyo has more invested than just wanting the food they are promised by the villagers.
It should be said that there is a great deal of big acting going on in the film that really separates most of the villagers from the samurai who are rather low key save for Kikuchiyo. Toshiro Mifune though really is a master at this rather broad approach, since he firstly does not forget to still have subtle aspects to the performance that keep his performance properly grounded, but as well being able to act this big is a talent not seeming completely overblown, and Mifune most certainly has this talent. For example one great scene of Mifune is when Kikuchiyo chews out the other samurai for their comments regarding the farmers of the village they are protecting.
In this scene Mifune is full force in his intensity and intimidation as he rattles on about his anger toward the remark against the farmers. His hatred of the disregard of the farmers is violent and vicious and Mifune does not lose a beat as he goes off on Kikuchiyo full loud monologue. While he handles this scene in a very big fashion indeed, Mifune never fails though in the same moment to offer smaller hints as to an underlying sadness within Kikuchiyo since really all of this anger comes from the fact that Kikuchiyo himself came from a farming family.
During the all important battle scenes it is hard not to watch Mifune he is consistently entertaining and effective in the role. He portrays Kikuchiyo as a man with almost a death wish the way he throws himself into the battle field seeming almost psychotic at times when he basically eggs on the bandits to aim for him. There is never a moment where Kikuchiyo does not seem to be throwing himself head first into the fray. Mifune is able to through in just the right amount of humor in his performance through his manic approach. Mifune though is able to with ease bring humor at the same time in showing Kikuchiyo's genuine, and very passionate in regards to fighting the battle.
This is especially powerful performance by Mifune as he uses his energy in his performance to become both a very enjoyable comic relief at times, but also does manage to bring to life the very heartbreaking character that is Kikuchiyo. It is indeed a very manic approach as Mifune shows not the slightest hesitation in any scene whether Kikuchiyo is flopping around the battlefield, or is raging in anguish over witnessing an event that mirrors something in his own past. There is never a disconnection in any moment or any facet of Mifune's work here. It is simply a great performance that contributes so much to this amazing film.