I bought a phone charger at a duty-free store in Incheon. Can I open and use it before my flight to the US?
Yes, you should be able to use the phone charger you purchased at the duty-free store in Incheon before your flight to the US. Duty-free stores sell products that are exempt from certain taxes and duties, but there are generally no restrictions on using the products immediately after purchase. However, if you have any doubts or concerns, it's always a good idea to check with the airport or airline staff before using the charger.
Makes sense. Now, the flight is very long (14 hours), what could I realistically read in this timeframe? I'm a fan of manga and sci-fi comics (Transmetropolitan, Moebius works).
In 14 hours, you could realistically read several volumes of manga or sci-fi comics. It really depends on the length and complexity of the works you choose. Here are a few estimates to give you an idea:

- Manga: A typical manga volume has around 200-300 pages, so you could probably read 4-6 volumes during a 14-hour flight. Of course, this also depends on the pacing of the story and how quickly you read.

- Sci-fi comics: Transmetropolitan is a series of 10 volumes, each with around 144 pages, so you could potentially read the entire series during the flight if you read at a steady pace. Moebius works vary in length, but some of his longer works like The Incal have around 300 pages, so you could potentially read 2-3 works of that length during the flight.

Of course, these are just estimates and everyone reads at a different pace. You may also want to take breaks to stretch your legs, eat, or watch a movie during the flight, so factor that into your reading time as well.