[ps67]

I don't know if it is the correct way but it works for me. It is similar to collection with a slight difference. Create a new custom column, for example Subtitles, then in the "find name" field write #subtitle (my calibre setting is in Italian so I translate and may be not exactly the same but I think You can understand).

In the driver settings of the plugin, in the part of "Metadata, on device & advanced" check the subtitle button and write {#subtitle}

When connecting Your Kobo it should give to You the subtitle, not the first time after invoicing a book but the second, when the book is already in the database, of course If You decided of modifying database whenever You connect Your Kobo to calibre.

In this way You can obtain series - using the apposite column of calibre - and subtitles (I know, very few books have both but they are not the same thing).

You can also change manually it, with others metadata, using the "update metadata in device library", also check Subtitle button and write again {#subtitle}