\defineframed[StyleChapterFramed][
  frame=off,
]

\define[1]\StyleChapter{%
  \StyleChapterFramed{%
    \framed[align=right, frame=off]{%
      \startoverlay {
          \getfirstcharacter{#1}%
          \firstcharacter%
        }
      \stopoverlay
    }
  }
}

  \setuphead[chapter][
    deeptextcommand=\StyleChapter,
  ]

\starttext

\startfrontmatter
  \completecontent
\stopfrontmatter

\startbodymatter
  \startchapter[
    title={Chapter},
    reference=sec:chapter,
  ]

  \startsection[
    title={Section},
    reference=sec:section,
  ]

  \startsubsection[
    title={Equipment},
    reference=sec:equipment,]
    \input knuth
  \stopsubsection

  \stopsection
  \stopchapter
\stopbodymatter

\startbackmatter
  \completeindex
  %\placeindex
\stopbackmatter

\stoptext

