I'm not sure just how you mean "resistance," but the internal politics of Japan in the period leading up to WW2 were extremely chaotic in many ways, and (to your question) there were frequent political assassinations, as well as attempted coups and putsches.

There were many fault lines and the process defies easy categorization or summary, but some of the major divisive issues were how to relate to the West, whether to retain the democracy of the preceding "Taisho" period or switch to a more autocratic model of government, and how to relate to neighboring countries, especially China. Over time, the autocratic, imperialistic, anti-Western forces gradually achieved total power over government policy.

You can characterize the opposition to this process as a "resistance" only by ignoring that, at the beginning of Japan's slide into its so-called "dark valley" period, the pro-democracy, anti-imperialist factions were, broadly speaking, the ones in control. In effect, the imperial, anti-Western, autocratic groups *were* the resistance, and they gradually bullied their way into more and more power over time until they finally took over. To give a few examples:

- Prime Minister Hamaguchi Osachi was elected in 1930, with the Emperor's support, with a mandate at least partly based on the Emperor's desire to reassert civilian control over the military. Hamaguchi was in office less than a year before he was shot by members of an ultranationalist cabal. He survived, and was even reelected, but eventually died of conditions relating to his gunshot wounds.

-Not even two years later, Prime Minster Inukai Tsuyoshi warned the Emperor that the military had effectively escaped any oversight or responsibility, and shortly afterward was shot dead in his own house by 11 naval officers, which you would have to say rather proved his point.

- An example of the kinds of things the two dead PMs were concerned about is the Mukden Incident, in which the Kwantung Army, acting without authorization, invaded and conquered all of Manchuria. Later, Hirohito would admit that "if he had desired to be a constitutional, peace-loving monarch, he should have taken a stand" during this period.

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- In 1936, the so-called "February 26 Incident" consisted of a coup attempt by army personnel, in which two former prime ministers and various others were killed and attempts were made to seize control. Although the coup failed, it had the effect of essentially establishing a military veto over the selection of civilian officials. This one is unusual in that some people were actually executed or imprisoned for taking part in it, but in the end it still had the effect of further weakening the civil authority.

Many other examples could be given, but what's striking about them is that the perpetrators generally suffered very minimal consequences. Military officers who betrayed their oaths and tried to overthrow the government were either left entirely alone, or merely sent to stand in the corner for a bit.

As time went on, politicians who were opposed to the militarist agenda were gradually painted into a smaller and smaller corner. Even Yamamoto Isoruku found his life in danger because of his political positions, and he was given command of the combined fleet, at least in part, because floating on a ship in the harbor surrounded by loyal navy personnel would make him more difficult to assassinate.

So, there was indeed a battle against imperialism, militarism, and autocracy in Japan, but by the time war broke out it had already been lost for years. In 1944 and 1945, as Japan's cities burned and starved and her soldiers died like flies, neither political nor popular resistance to the war or the militarist program was meaningfully possible. Even when the Emperor finally intervened to compel a surrender, the military returned to its old playbook from the 1930s, and a coup on that model was attempted, and even succeeded in occupying the palace grounds for hours. But it didn't work out, and in the end, democracy and anti-militarism were reimposed on Japan by force.

Sources: Ben-Ami Shillony, Revolt in Japan: The Young Officers and the February 26, 1936 Incident.

Daikichi Irokawa, The Age of Hirohito: In Search of Modern Japan

Oka Yoshitake, et al. Five Political Leaders of Modern Japan: Ito Hirobumi, Okuma Shigenobu, Hara Takashi, Inukai Tsuyoshi, and Saionji Kimmochi