Regarding durability, I'm sure the Trek Domane SL5 2021 can take a bit of a battering, but I personally would be wary of taking anything with a carbon frame on a tour.
I did a 3.5 week tour of Japan myself last year (best time of my life!) and no joke, I smashed one of the seat-stays into a bicycle gate thing between Osaka and Kyoto on my first day of riding. Luckily I took a steel frame bike, but I hit it hard enough that I'm sure a carbon frame would have been ruined. It had (and still has) a sizable bend in it, but it survived the trip without any trouble, and still does me good as an occasional backup commuter.
Point being, when you are touring, your bike is your everything, and if it gets damaged, your holiday is ruined (especially if it's only a couple of weeks). A steel frame will be heavier, but if it takes a hit, it's much more likely to survive and be rideable. I don't think you can have that kind of confidence for carbon (or even aluminium for that matter).
Regarding comfort for touring, certain bikes are built with a frame geometry that has comfort in mind, but you can make many bikes acceptable for touring comfort by adjusting them properly to your body. The bike I took was probably more of a racing geometry, but with the right adjustments and good seat I was fine. In fact, if I were you, I'd spend a big part of my effort on getting a seat that suits you really well. I'd recommend a Selle SMP, but seat selection is a very personal thing.
Good luck with your tour, Japan is an amazing place to see by bike, and a great place for a first tour - you're never more than 10km form a conbini!
Image from: http://regex.info/blog/2015-06-26/2592