spirit, steam radical (no. 84)
气 centers on an invisible vital force: spirit, energy, or vapor. The radical sense is the same visible shape used as a component in other characters, often related to gas or atmosphere.
气 is a pictograph of rising vapor or breath, with the modern form preserving a stylized cloud-like shape.
The top horizontal line is like a lid, and the curved lower strokes are rising steam or breath escaping. Picture a pot releasing invisible spirit: 气 is that vapor.
For キ, imagine a key unlocking a hidden spirit: key -> キ, and the vapor rises as the lock opens.