Being a collection of clipped and scaled glyphs, it is very font dependent. Obviously, this is not creating a ligature, but merely piecing together an image.
\documentclass{article}
\usepackage{stackengine,trimclip,graphicx}
\newcommand\Gi{\clipbox{0pt -.1ex .65ex -.1ex}{6}\stackengine{0pt}{%
\clipbox{.52ex -.1ex 0pt .4ex}{6}}{\scalebox{2}[1]{\clipbox{.52ex 1.1ex 0pt -.1ex}{6}}}%
{O}{l}{F}{F}{S}\kern-.75ex \i}
\newcommand\ia{\scalebox{-1}[1]{\Gi}}
\begin{document}
\Gi o\ia
\end{document}

A more complex clipping (different vertical scales of the pieces/parts), again in Computer Modern
\documentclass{article}
\usepackage{stackengine,trimclip,graphicx}
\newcommand\Gi{\clipbox{0pt -.1ex .65ex -.1ex}{6}\stackengine{0pt}{%
\clipbox{.52ex -.1ex 0pt .45ex}{6}}{\scalebox{2}[1.22]{\clipbox{.55ex 1.14ex 0pt -.1ex}{6}}}%
{O}{l}{F}{F}{S}\kern-.75ex \i\kern-.1ex}
\newcommand\ia{\scalebox{-1}[1]{\Gi}}
\begin{document}
\Gi o\ia
\end{document}

and then using Baskervald (2 variants):
\documentclass{article}
\usepackage{stackengine,trimclip,graphicx}
\newcommand\Gi{\clipbox{0pt -.1ex .77ex -.1ex}{6}\stackengine{0pt}{%
\clipbox{.50ex -.1ex 0pt .4ex}{6}}{\scalebox{1.7}[1.4]{\clipbox{.545ex 1.37ex 0pt -.1ex}{6}}}%
{O}{l}{F}{F}{S}\kern-.66ex \i\kern-.1ex}
\newcommand\ia{\scalebox{-1}[1]{\Gi}}
\usepackage{baskervald}
\begin{document}
\Gi o\ia
\renewcommand\Gi{\clipbox{0pt -.1ex .85ex -.1ex}{6}\stackengine{0pt}{%
\clipbox{.42ex -.1ex 0pt .49ex}{6}}{\scalebox{1.83}[1.83]{\clipbox{.49ex 1.377ex 0pt -.1ex}{6}}}%
{O}{l}{F}{F}{S}\kern-.68ex \i\kern-.1ex}
\Gi o\ia
\end{document}
