notes

Function NormalizeKatakana(ByVal text As String) As String
Dim i As Integer
Dim result As String
result = ""

For i = 1 To Len(text)
    Dim ch As String
    ch = Mid(text, i, 1)
    Dim chCode As Integer
    chCode = AscW(ch)
    
    ' 次の文字が濁点 (゛: U+3099) または 半濁点 (゜: U+309A) の場合
    If i < Len(text) Then
        Dim nextCh As String
        nextCh = Mid(text, i + 1, 1)
        Dim nextChCode As Integer
        nextChCode = AscW(nextCh)
        
        If nextChCode = &H3099 Then ' 濁点゛
            If chCode >= &H30AB And chCode <= &H30DB And (chCode Mod 2 = 1) Then
                ch = ChrW(chCode + 1) ' カタカナの清音 → 濁音
                i = i + 1 ' 濁点をスキップ
            End If
        
        ElseIf nextChCode = &H309A Then ' 半濁点゜
            If chCode >= &H30CF And chCode <= &H30DB And (chCode Mod 2 = 1) Then
                ch = ChrW(chCode + 2) ' ハ行の清音 → 半濁音
                i = i + 1 ' 半濁点をスキップ
            End If
        End If
    End If
    
    result = result & ch
Next

NormalizeKatakana = result

End Function

' テスト用サブルーチン
Sub TestNormalize()
Dim testStr As String
testStr = "カ゛キ゛ク゛ケ゛コ゛_シ゛ス゛セ゛ソ゛_タ゛チ゛ツ゛テ゛ト゛_ハ゛ヒ゛フ゛ヘ゛ホ゛_ハ゜ヒ゜フ゜ヘ゜ホ゜"
Msgbox "Before: " & testStr & Chr(10) & "After: " & NormalizeKatakana(testStr)
End Sub