With Calibre, assuming a common sane for-Kobo setup, chances are you won't ever get Nickel to use the book's own metadata, @davidfor's excellent Kobo driver handles all of that for you straight from Calibre's own metadata, injecting all of it directly in Nickel's db
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(Which means the situation I explained above, where the on-device-book's OPF might be horribly (or slightly ;p) broken, would be silently fixed by the driver, as long as Nickel managed to import it in the first place).