Hitler was very clear on his idea of the master race and white supremacy so how did the Japanese feel being on the side of someone who most likely did't view asians as equals?
Not an expert, but it has been asked before
According to /u/Subs-man's answer, the Japanese was not content with Hitler's anti-Semitic policies. Please see Subs-man's answer for more information.
Edit: As requested by the moderators. Added Link to the highest ranking answer and notified Subs-man about the new discussion.
I can offer a bit more context for racism in Japan prior to WWII. Someone in the previous thread makes the claim that Japan never really supported eugenics. But eugenics and scientific racism did have a foothold in Japan from as early as the Meiji era. Mitchell's "New School Geography" was used as a textbook in Japanese schools, and divides races and cultures into five categories: "savage, barbarous, half-civilized, civilized, and enlightened." Europeans and Americans are categorized as civilized, but Japan is categorized as "half-civilized." Furthermore, there were a number of Japanese scientists who ascribed to eugenics: Fukuzawa Yukichi cites Francis Galton's Hereditary Genius, and Takahashi Yoshio promoted "white and yellow interbreeding" in The Theory of improvement of the Japanese Race.
The gist of a lot of these writings seems to be that Japanese scholars were simultaneously looking up to what they saw as the superior achievements of the "European race" and replicating European imperialism and racism in order to justify their own imperialist projects, casting other groups in Asia (and even out-caste groups within Japan) as members of "inferior races." There are interesting accounts of a World's Fair exhibition in Japan that put Okinawans and Taiwanese individuals into what was effectively a "human zoo" intended to showcase primitive peoples.
My own interest in this subject deals with the way that literary translations dealt with the representation of race, so most of my sources are about that. I particularly enjoyed Robert Tierney's “Othello in Tokyo: Performing Race and Empire in 1903 Japan” and Yoshihara Yukari's “Japan as Half-civilized: an early Japanese adaptation of Shakespeare’s Merchant of Venice and Japan’s construction of its national image in the late nineteenth century.” But Yuehtsen Juliette Chung's Struggle for National Survival: Eugenics in Sino-Japanese Contexts, 1896-1945 seems to address the subject of eugenics more explicitly. (I haven't read this one, but I looked it up for more background info on Japanese eugenicists)
I'd actually like to ask a follow-up question, though this may be a for a separate post:
I feel like all the emphasis on Hitler obscures the fact that there had to be many, many others who both inspired and directly contributed to his ideas; and to Nazi doctrine more generally. It's never just one man. So who were the "intellectuals" of the Nazi Party, the ones who built the ideology?