Lots of options:
I doubt that only 5+ years after their reform they would be this powerful, but for ASB:
-Korea resists Japanese influence, allies with Russia in 1905, wins the Russo-Korean-Japanese war, Japan loses its Influence in the region, Japan loses Tsushima island to Korea, does not gets half of Sakhalin, and the Kurils are given back to Russia, with better dominance in East Asia, i think the White Russians would be better at establishing a Govt. In Exile in the East like they attemted in OTL, but i doubt tthat Stalin would allow a White Russian govt bordering the USSR, would Germany offer Japan to ally with them in the Great War in return for their colonies? would Japan become isolationist?, let's discuss. * Would Japan still be seeking ambitions outside of East Asia?, instead of getting countries solely in East Asia, they dedicate themselves fully for the Pacific, i think that if so, the Pacific War would have started earlier (1930's or so), with the US under a depression, they can't get the Phillipines back, they stay Japanese until the US gets their shit together and gets it back.
-Russia still loses, the modernized Korea resists Japan in a big war, but Korea still loses, it'd be hard for Japan to directly annex a westernized country, instead of annexing them, the Korean Empire becomes another Manchukuo, nothing else changes today as long as i can confirm.
Instead of being directly invaded, Korea is treated by Japan like Thailand, they're not puppetized, just fearing another war, they comply with their demands, the Pacific War lasts longer (Jan-Feb 1946), and Korea is fully under Communist control, no North Korea, no Korean War, a lot changes today. * The United DPRK might not be so brutal as it is today, one of the main reasons they're so dictatorial is because they are so small and isolated, i think that Korea would get China-style reforms, and become a "communist" economic power today, at least in their region. * Japan would get more Communist influence, but not become one, because the US are under their nose even more in this TL.