>>   1. M-<
>>   2. C-x n n
>>   3. C-M-%
>>   4. M->
>>   6. C-x n w
>
> Forgot step 0,
>
> 0. C-SPC

What you described is a feature known in other editors as
"Current selection only".  In Emacs you don't need to use
`C-x n n' and `C-x n w' because `query-replace' limits the
search to the selected region without the need to narrow it.
However, other editors also provide another feature to replace
backwards like you can see in e.g. OpenOffice etc.