UnsafeToTitleCase.cs

static unsafe void ToTitleCase(string input)
{
    if (input.Length == 0)
    {
        return;
    }

    fixed (char* chars = input)
    {
        bool startOrNotLetter = true;
        for (int i = 0; i < input.Length; i++)
        {
            char current = chars[i];
            if (startOrNotLetter)
            {
                startOrNotLetter = false;
                if (char.IsLower(current))
                {
                    chars[i] = char.ToUpperInvariant(current);
                }
                continue;
            }

            if (char.IsUpper(current))
            {
                chars[i] = char.ToLowerInvariant(current);
                continue;
            }

            startOrNotLetter = !char.IsLetter(current);
        }
    }
}