The LaTeX command for yen (¥) is \textyen (yen sign in text; amssymb's \yen is the math-mode form).
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Write \textyen in normal text, outside math mode. It is part of core LaTeX, so no extra package is required.
\textyen is a text command: inside a formula it needs \text{...} from amsmath. With XeLaTeX or LuaLaTeX you can also type ¥ directly.
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Text symbols in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \textyen in normal text; it needs no extra package. For example, \textyen.
None: \textyen is built into LaTeX, so no extra package is required.