\listfiles
\documentclass{jsarticle}
\usepackage{textcomp}
\usepackage{ascmac}

\newcommand{\Yen}{Y\llap=}
\newcommand{\yyen}{{\ooalign{Y\crcr\hss=\hss}}}

\begin{document}

\yen %ascmac.sty

\Yen

\textyen %texcomp.sty

\yyen

\end{document}
