Is this question concerning US Soldiers (US Army) or are you calling all servicemen "soldiers"?
World War II in the Pacific Theater was a NAVAL WAR. Consequently, the vast majority of casualties were US Naval men, which would include the US Marine Corps.
The only army casualties were US Army Air Corps flyers stationed in the Pacific and CBI theaters and the Philippines which fell under GEN MacArthur's command.
Since the Pacific Theater of Operations (aka Pacific Ocean War) was a naval war, casualties were much less than in the European Theater because massed armies couldn't operate on the surface of the water (on the surface of the ocean). Less than 60,000 US military men (all branches) were KIA in the PTO; of which approximately 14,000 were US Marines.
For example, if one US warship was sunk, like the USS Indianapolis heavy cruiser, and about 1,000 US sailors are killed, then that would equate to roughly one full US Army ground battalion or two US Army understrength battalions being lost in battle. Since the vast majority of fighting occurred under that scenario in the PTO casualties were less than the ETO theater, since only 1 or 2 or 3, etc. cruisers might be sunk (lost) during a battle in the PTO. Land battles in the PTO were almost always Regimental size fights, no Division or Army level engagements: Islands simply didn't have enough room to maneuver large armies as the ETO did.
100000
Mainly as a defense against Japan or other imperial powers that might come along
The Meiji restoration turned Japan in to a modernized imperial power.
Japan's conscription policies gave the Japanese army access to manpower and was able to install within its recruits the traditional Japanese culture the policy of total obedience to the Japanese imperial system. By 1937, its military expansion program created to 24 divisions, and 54 air squadrons. By 1941 Japan had 133 air squadrons and had an army of over one million troops. This was backed by two million trained reserves.
Imperial.
At the beginning of WW2, the most powerful navy in the world. Japan did not have the most powerful navy in the world, the British Royal Navy was instead considered the global maritime superpower until a few years after WWII. Japan, however, was indeed a very powerful military power with a massive navy roughly equal to that of the United States at that time.
Imperial Navy.
A military officer (Army, Navy, Marines, or Air Force) of an Imperial Country, such as Imperial Japan during WW2. An imperial nation is normally headed by a Monarch; an Emperor or King.
Japan was an imperial state, with an emperor that was thought of as a god. Mainly it was a Military Dictatorship.
Imperial Guard - Japan - was created in 1867.
Japan's Imperial Conspiracy was created in 1971.
Mainly as a defense against Japan or other imperial powers that might come along
Military historians consider that the tide turned against Japan with the Battle of Midway, and that the Allies had the upper hand from then on.
Imperial Prize of the Japan Academy was created in 1947.
I am not sure which era you are asking about. During World War II, for example, Japan was part of the Axis, along with Germany and Italy. Japan's military was capable of delivering devastating attacks: in fact, the Imperial Japanese Navy mounted a surprise assault on a US naval base at Pearl Harbor (in Hawaii) in December 1941 that led the United States to enter the war. After Japan and the other axis powers were defeated in 1945, their Imperial Military was dismantled. Japan subsequently established a new military-- called the Japan Self-Defense Forces, which were mainly empowered with maintaining peace and order, rather than embarking on any aggressive maneuvers against other countries. These days, Japan's current prime minister, Shinzo Abe, has gradually begun to spend more money on purchasing new military equipment and enhancing the country's defense, although certainly not to the degree that was seen during World War II.
The Meiji restoration turned Japan in to a modernized imperial power.
Russia + China
A centralized (strategic) region to place military forces (bases); against the proposed enemy, Japan.