Let's say the Chinese army was way much more competent than OTL, as a result, Japan could not gain any territory from China and Korea during the Second Sino-Japanese War 1895. (With such an outcome, Taiwan remained Chinese, Sakhalin was already ceded to Russia in 1858.)
Japan faced a situation much similar to what the British faced after the lost her last bridgehead on continental Europe, Calais. She were forced to become an Maritime Empire.
A strong China (Qing? Beiyang RoC? Empire of China? up to you.) was anti-Russia and somewhat pro-Japan, and she defined herself a land power with Russia as her potential enemy. China limits its navy to just enough to defend its coast, with 1 or 2 battleships and latter a moderately-sized submarine fleet. But her army was state-of-the-art.
Under such circumstances, Japan did the opposite. She opted for a strong navy and weak army, and aimed elsewhere for colonial expansion.
Let's say trade with a friendly China could compensate the loss of Korea and give Japan a better economy than OTL to fund such a great navy.
Your task is to make Japan's colonial empire as large as possible, and evaluate the possible impact of such an Empire.
A Japanese Southeast Asia? A Japanese Australia? A Japanese South America? A Japanese Africa?
I do not recommend Siberia, for this will make China (ITTL Japan's ally) feel threatened.
You have from 1895 to 2012 to make your empire.