I'll be traveling this week from Málaga (Spain) to Tokyo, with Alitalia. There's an 8-hour stopover at Rome Fiumicino. Am I supposed to pick up my bags and check them in again at Fiumicino?
Ask when you check in and drop off your bags; unless it's an overnight connection, your bags will likely be checked through to Tokyo. If you prefer to be able to claim your bags, you can ask the airline to short-check your bags to FCO (Rome) and then check them again when you return for your Tokyo flight.– Jim MacKenzieSep 29, 2017 at 22:52
If it's with the same airline or the same alliance, your luggage will go all the way to Tokyo. The number of hours in transit doesn't really matter. In Málaga, at check-in, the employee will ask you where you're going, and whether you want to check your luggage to your final destination. Say yes, and you can pick up your luggage in Narita.
You will have to ask your airline about this on this specific itinerary. With 8 hours, probably not, unless it's overnight.
I have had to collect luggage on an overnight connection ~8 hrs before so...