It's the wind. Check out Windy.com and dial the altitude up to FL340. Lots of funky vortices that a polar flight from Japan to Europe would have to fly into head-on. For the same reason, flights from Japan to the US are flying almost due east, instead of the usual great circle route over Alaska.

Also this: https://www.flyertalk.com/forum/trav...l#post35715334

Over 15hrs for HND to CDG. Getting to and from Japan is very long haul nowadays.
And to think I used to dislike the old 12hr flights across Siberia.

Thank you for looking into it, that definitely makes sense. Even the route we came the seatbelt sign was illuminated for the final 2 hours of flight. I ended up having to disembark in my comfy jogging suit that I wear to sleep on longhauls as wasn't allowed to use the lavatory to get changed prior to landing.

Stupid question, but I thought I might ask anyway in case someone had more insight:

does anyone know why KL doesn’t fly into/out of HND? I’m assuming it has to do with limited slot allocations and them not chasing it as aggressively as AF?

very likely the reason.

HND is slot restricted and, between 1978 and 2010, was operated mostly as a domestic airport; the construction of Narita as the "international" airport for Tokyo was hugely controversial and led to civil unrest.

While international flights have been gradually returning, it seems that slots to international territories, when made available, are divided equally between Japanese and foreign carriers. Given that no Japanese airline serves the Netherlands, it would appear that AMS is unlikely to be a direct route from HND anytime soon.

if your plane crosses the date line while flying, you will arrive 24 hrs later than if you managed to get there without touching the.line. You will also have aged an extra day. Any sushi on board will instantly go bad.

This is of course a joke. The date line has no bearings on navigation. Your plane will take the fastest way there, across the line or not.