Japan and Germany were superpowers before world wars broke out. They were ahead of what the Allies were for a long time. Look at the history of victories Japanese have had against European colonists. They adapted the latest standards and continued to refine them, making them a superpower compared to Dutch, British, Beligians, French etc all of whom have been thrashed by them.
However, the official Superpower word was used only after WW2.
Japan had its share of military victories but that doesn't mean superpower. In that era, that status required the backing of an immense industrial system which Japan lacked though it was still capable. A nation with the potential of "superpower" capabilities are sometimes hard to express to a great extent during baseline activity. Superpower is the combination of the fundamental base with its global expression (it can stay dormant until certain events)
The true power was America even before the outbreak of WW2, it was just dormant in its industrial scale military expression and military projection but was still capable as seen with numerous interventions. It was hidden away in civilian industries and production. No other nation came close to its production capabilities.
1938 vs peak production
USA's production increased 87% by 1944
UK's production increased 27% by 1943
Germany's production increased by 25% by 1944
Japan's production increased by 17% by 1942
Most major industrial nations of WW2 had their productions increase during the war and within a similar range (17-27% for the given example), US was the outlier with a near doubling of GDP. This shows all other nations were near their potential while the US had more resources to draw upon, in addition to a safe continental homeland.
https://en.wikipedia.org/wiki/Military_production_during_World_War_II
Britain was even a bigger power before WWII. She lost her status after the Suez crisis
Britain had much more colonies and dominions under its control and influence in addition to a more global presence but by the late 19th century the US was quite capable in large scale military interventions.
https://en.wikipedia.org/wiki/Timeline_of_United_States_military_operations
UK baseline military spending pre-WW2 was 2.5-3%, spiking at each outbreak.
US baseline military spending pre-WW2 was around 1% of GDP, it was spending very little on its military pre-WW2 with exceptions of certain events.
The US surpassed UK's GDP by around 1870's but if we are to count the colonies and dominions then right before WW2 their GDP were similar with a slight edge to the US. American power during WW2 was mainly the expression of their civilian industries utilised for military purposes. WW2 was a turning point, a point which industries transitioned from civilian to military. The large industrial base was present and built up decades before the war while the British Empire was in decay.
Japan cannot be a superpower with its own landmass and population. It needed to control and access the resources of Asia, that was the whole point of invading China and South East Asia, natural resources, human resources and strategic depth. In other scenarios it can only attach itself to another power. In the case that it cannot control East Asia or other sizeable regions and the oceans, it cannot become a superpower. The Qing royals were persuaded to marry Japanese nobility, which later occurred. Although this is speculation, I think the plan was eventually intermarry royal families and claim the whole region, then move the capital to China. Various ambitious Japanese leaders throughout history had these plans, there was a case where one wanted to establish a Naval Empire based out of Ningbo.
Germany cannot be a superpower with its own landmass and population either, it needs continental Europe to do so. It fought WW2 using liquefied coal gas (92% of aviation fuel, 50% of petrol) from the lack of a diverse base of natural resources. 4th Reich is possible if it keeps EU together or some other variation.
https://en.wikipedia.org/wiki/Coal_liquefaction
Japan and Germany have strong industries with great technologies but not of superpower status, that requires a additional pieces that are missing. Japan was never recognised as a superpower because it never was one and still lacks the fundamental factors to become one.