Would have such a 'closed' country put up a serious fight when the Russians leaned on them circa 1900 ? IIRC, the modernised IJN totally stomped the Imperial Russian fleet, causing a major flutter of butterflies and, IIRC, significantly contributing to the Russian Revolution. Recall the traumatised Russian navy proved a hot-bed of revolution, provided fire-support...
Else, the Japanese islands would be Imperial Russian, out-right or as protectorate. Would the-then Japanese Emperor's son have been married off to eg Anastasia ?
( Cue different take on 'The King & I' for musicals !! )
Apparently a nice man, perhaps time in the West and, surely, Australia, Singapore, Hong Kong, Shanghai etc would have made him intolerant of the 'imperial cocooning' that let the militant faction run Japan in OTL...
Had there still been a Russian revolution, perhaps East of the Urals, Siberia etc, would switch allegiance to Anastasia ? And the White Russians would have support from the Far East ?? IIRC, the Revolutionaries' terror was that even one of the 'immediate succession' Romanovs would escape. Hence their massacre...
( FWIW, I worked with a nice guy who, to his considerable embarrassment, was twenty-something-ish in line to Romanov crown. Pete_W wanted nothing of it, but his parents, passionate succession-watchers, kept trying to pair him up with wannabe princesses to boost their combined ranking. NOT funny... )
Not modernised, no vast need for iron, fossil fuels etc mean Japan has no urge to set up a 'co prosperity' grab in the area. Mildly modernised, they can trade. FWIW, they might help open up Siberia !!
Uh, no Manchurian atrocities ? No CBW research on prisoners ?? No 'Pearl', no Bataan 'Death March', no H&N nukes ? In fact, 'Romanov' Japan would be allied to the UK via Victoria's cousins !! Even with a Revolution, they'd be supporting the Allies rather than the Axis, running supplies to the North Pacific ports...
So, no Pacific war beyond a few German commerce raiders, no need to deploy & lose UK, Dutch etc armies, navies, air-forces, battle in Burma etc etc.
And, without Pearl, would US have come in so promptly and forcefully ? Would they have stayed 'mostly neutral', held to lease-lend ??
Sorry, this ATL now has far, far too many butterflies for me to track further.