\documentclass{article}
+\usepackage{lltjext}
\usepackage{luatexja-fontspec}
\setmainjfont{IPAmjMincho}
\setmainfont{Crimson}
abc𛀙゙「𛀬゙𛀰゙」𛀸゙𛀿゙𛁅゙𛁈゙𛁛\\
abc𛂞゚𛂟゚𛂠゚𛂡゚𛂢゚𛂣゚𛂤゚𛂥゚𛂦゚𛂧゚𛂨゚\\
This Latin text should be rendered in crimson.
+
+\parbox<t>{20\zw}{%
+abc𛀐𛀑𛀒𛀓𛀔𛀕𛀖𛀗𛀘𛀙𛀚𛀛𛀜𛀝𛀞𛀟\\
+abc𛀙゙「𛀬゙𛀰゙」𛀸゙𛀿゙𛁅゙𛁈゙𛁛\\
+abc𛀙゙「𛀬゙𛀰゙」𛀸゙𛀿゙𛁅゙𛁈゙𛁛\\
+abc𛂞゚𛂟゚𛂠゚𛂡゚𛂢゚𛂣゚𛂤゚𛂥゚𛂦゚𛂧゚𛂨゚\\
+This Latin text should be rendered in crimson.
+}
+
\end{document}