Thank you for doing the right thing.
Please take a look at the electronic item. Many of them contain a serial item, e.g.
at the bottom, behind the battery, sometimes on the side. If the item does, you may contact the manufacturer. In many cases, they will have an owner listed through some channel (or may be able to trace the store in which the item was sold and through that reach the owners)
You can also contact the airline, give the day/time/description of the people, and they may be able to try and link it with a record (or video recording) of the couple to return it
^ for trying!
Added: NRT's lost and found service in Terminal 2 can be reached at +81(0)476-34-5220. [Just in case, terminal 1's lost and found is +81(0)476-32-2105]