Why the specific spelling "一つひとつ"? I'm reading a book and the author keeps using the spelling "" for "one-by-one". I found this a bit curious: The word itself is just a doubled , so why not spell both parts the same? Does writing it that way convey a certain nuance which or 11 do not?

This is a matter of personal taste. If the author did this intentionally, I believe they were trying to emphasize the nuance of by covering various possible spellings. Similar examples include and . One may also argue that switching kanji/kana too much in a single word is visually displeasing, but I personally doubt that is the main reason.

Here are the hit counts of BCCWJ:

* : 604
* : 1005
* : 293
* : 5



* * *

**EDIT:** This is not limited to ...

* : 224; : 193; : 9; : 0
* : 2; : 183; : 9; : 0
* : 8; : 24; : 3; : 0
* : 823; : 354; : 4; : 0



Maybe the users of are treating the second part somewhat like a long okurigana...? I personally do not do this, but it is true that there are writers who like this style.