Sun and Steel by Japanese writer Yukio Mishima is an extended essay that uses first-person narration to discuss the craft of writing and explore the relationship between mind and body. At the essay's outset, the writer disavows that the "I" used in the essay is himself but is instead a concept that does not relate back to him (and so can be taken as a fictional construct).

The essay begins by contending that words are corrosive and, like any corrosive material (such as stomach acid), can eventually corrode itself. Words do not need to depict reality, which, for the young narrator, is represented by the body. Words transform reality into abstractions so that the mind can contemplate it. In this process, words change reality. When the writer was young, he thought that the body was a reality outside of himself.

He watches a group of street performers and finds a character whom he deems suitable as a subject for his writing, which will attempt to capture the perfect body form. This performance inspires the writer to address himself to the task of discussing sun and steel as metonyms for the mind and the body. The narrator also remembers encountering the sun for the first time during the summer of the end of World War II. He associates the sun with death and becomes nocturnal until a trip abroad in 1952.

In counterpoint to his nocturnal self, the narrator begins lifting weights, developing a close relationship to "steel," and remarks that the physical development of the body is remarkably similar to that of the mind—slow and extreme. Strength and steel, the narrator observes, are interdependent and so akin to the condition of an individual living in the world. The narrator admits to longing for an early death and to becoming intellectually bored and upset amid the postwar world.

The narrator realizes that what he lacked was the identification with a group, without which a truly tragic death is impossible. The group that allows for tragic death is, naturally, a group of warriors. Once the narrator joins this group, it is, for him, like crossing a bridge with no prospect of return.

In the writer's epilogue, he describes flying in an F104 supersonic plane around Mt. Fuji. This is a transformative experience for the narrator (who is a passenger), as it allows him to experience the sun bolting through the glass cockpit and also see the clouds more closely. He likens the clouds to a snake constantly swallowing its own tail. Like the snake that causes all polarities to vanish, the narrator imagines that the sun and steel (mind and body) will, too, become one when distant from the earth.