Compare character to character and put results in different column

Sub FindMissing()
  Dim c As Range
  
  With CreateObject("VBScript.RegExp")
    .Global = True
    For Each c In Range("C2:C" & Range("A" & Rows.Count).End(xlUp).Row)
      .Pattern = "(.)(?=.)"
      .Pattern = .Replace(c.Offset(, -1).Value, "$1|")
      c.Value = .Replace(c.Offset(, -2).Value, "")
    Next c
  End With
End Sub

Function Missing(Col1 As String, Col2 As String) As String
  Static RX As Object
  
  If RX Is Nothing Then
    Set RX = CreateObject("VBScript.RegExp")
    RX.Global = True
  End If
  RX.Pattern = "(.)(?=.)"
  RX.Pattern = RX.Replace(Col2, "$1|")
  Missing = RX.Replace(Col1, "")
End Function

Sub FindMissing()
  Dim c As Range
  
  Const AllDepts As String = "KCVEDPAFLSQBGXZ"
  
  With CreateObject("VBScript.RegExp")
    .Global = True
    For Each c In Range("C2:C" & Range("B" & Rows.Count).End(xlUp).Row)
      .Pattern = "(.)(?=.)"
      .Pattern = .Replace(c.Offset(, -1).Value, "$1|")
      c.Value = .Replace(AllDepts, "")
    Next c
  End With
End Sub

Function Missing(Col2 As String) As String
  Static RX As Object
  
  Const AllDepts As String = "KCVEDPAFLSQBGXZ"
  
  If RX Is Nothing Then
    Set RX = CreateObject("VBScript.RegExp")
    RX.Global = True
  End If
  RX.Pattern = "(.)(?=.)"
  RX.Pattern = RX.Replace(Col2, "$1|")
  Missing = RX.Replace(AllDepts, "")
End Function

Sub FindMissing()
  Dim R As Long, X As Long, Dept As String, Data As Variant, Diff As Variant
  Data = Range("B2", Cells(Rows.Count, "B").End(xlUp))
  ReDim Diff(1 To UBound(Data), 1 To 1)
  For R = 1 To UBound(Data)
    Dept = "KCVEDPAFLSQBGXZ"
    For X = 1 To Len(Data(R, 1))
      Dept = Replace(Dept, Mid(Data(R, 1), X, 1), "")
    Next
    Diff(R, 1) = Dept
  Next
  Range("C2").Resize(UBound(Diff)) = Diff
End Sub