documentclass{memoir}
usepackage{csquotes}
makeindex
usepackage{xpatch}
usepackage[indexing=true,authordate,backend=biber,language=auto,autolang=other]{biblatex-chicago}
usepackage{filecontents}

renewbibmacro*{bibindex}{%
  ifbibindex
    {indexnames{author}%
     indexnames{editor}%
     indexnames{translator}%
     indexnames{commentator}%
     ifkeyword{pri}{indexfield{indextitle}}{}
    }
    {}}


renewbibmacro*{citeindex}{%
  ifciteindex
    {indexnames{author}%
     indexnames{editor}%
     indexnames{translator}%
     indexnames{commentator}%
     ifkeyword{pri}{indexfield{indextitle}}{}
    }
    {}}

begin{filecontents}{pri.bib}
@misc{Kuṭṭanīmata,
  entrysubtype = {classical},
  author = {Dāmodaragupta},
  title = {Kuṭṭanīmata},
  related = {DezsoGoodall2012},
  relatedoptions = {dataonly,useeditor=false,usetranslator=false}
}
end{filecontents}
begin{filecontents}{sec.bib}
@book{DezsoGoodall2012,
  title = {Dāmodaraguptaviracitaṃ Kuṭṭanīmatam},
  subtitle = {The Bawd’s Counsel, Being an Eighth-century Verse Novel in Sanskrit by Dāmodaragupta, Newly Edited and Translated into English},
  editor = {Csaba Dezső and Dominic Goodall},
  translator = {Csaba Dezső and Dominic Goodall},
  series =  {Groningen Oriental Studies},
  number = {23},
  location = {Groningen},
  publisher = {Egbert Forsten},
  year = {2012}
}
end{filecontents}
addbibresource{pri.bib}
addbibresource{sec.bib}
DeclareSourcemap{
  maps{
    map{
      perdatasource{pri.bib}
      step[fieldset=keywords, fieldvalue=pri]
      step[fieldsource=title, final]
      step[fieldset=sortkey, origfieldval]
    }
  }
}
DeclareFieldFormat[misc]{title}{mkbibemph{#1}isdot}
newbibmacro*{pri:titleofauthor}{%
  ifentrytype{misc}
    {iffieldequalstr{entrysubtype}{classical}
       {ifbibliography
         {printfield{title}%
          ifnameundef{author}
            {}
            {setunit*{addspace}%
             bibstring{of}%
             setunit*{addspace}%
             printnames{author}%
             clearname{author}}%
          clearfield{title}}
         {printtext[bibhyperref]{printfield[citetitle]{title}}%
          ifnameundef{labelname}
            {}
            {setunit*{addspace}%
             bibstring{of}%
             setunit*{addspace}%
             printnames{labelname}}%
          clearfield{labeltitle}%
          clearname{labelname}}}
       {}}
    {}}
xpretobibmacro{cite}
  {usebibmacro{pri:titleofauthor}}
  {}
  {}
xpatchbibdriver{misc}
  {usebibmacro{bibindex}}
  {usebibmacro{bibindex}usebibmacro{pri:titleofauthor}}
  {}
  {}
begin{document}
Filler text autocite{Kuṭṭanīmata}.

Filler text autocite{DezsoGoodall2012}.

printbibliography[title=Primary Sources, keyword=pri,heading=subbibliography]
printbibliography[title=Secondary Sources, notkeyword=pri,heading=subbibliography]
printindex
end{document}

renewbibmacro*{bibindex}{%
  ifbibindex
    {indexnames{author}%
     indexnames{editor}%
     indexnames{translator}%
     indexnames{commentator}%
     ifkeyword{pri}{indexfield{indextitle}}{}}
    {}}

renewbibmacro*{citeindex}{%
  ifciteindex
    {indexnames{author}%
     indexnames{editor}%
     indexnames{translator}%
     indexnames{commentator}%
     ifkeyword{pri}{indexfield{indextitle}}{}}
    {}}

newbibmacro*{bothindex}{%
  indexnames{author}%
  indexnames{editor}%
  indexnames{translator}%
  indexnames{commentator}%
  ifkeyword{pri}{indexfield{indextitle}}{}}

renewbibmacro*{bibindex}{%
  ifbibindex
    {usebibmacro{bothindex}}
    {}}

renewbibmacro*{citeindex}{%
  ifciteindex
    {usebibmacro{bothindex}}
    {}}