Back to East Asian slavery in particular, though. I can't say all that much about China, because I don't have as much background there as with Japan, but the bottom line is: That concept changed constantly. There were different sources for slaves over time: debt slaves in the young state of Ancient China that meted out severe punishments to create order in this newly created thing; war captives in the Golden Age of expanding Medieval China, centre of the world; and whole ethnic groups in the multi-ethnic mega-state of Early Modern China. The history of China until the Revolution of 1911 can, simplified, be viewed as an ever-turning wheel of ethnic groups, religions, philosophies etc. changing in dominance, spinning around an axle of core values. That can, of course, be said about e.g. Europe as well, but I find that the changes in China, where no creed or philosophy was ever as powerful as Christianity or Islam, are more fluent. Thus, attitudes to social institutions like slavery could change fundamentally from dynasty to dynasty and even from ruler to ruler. Some tried to abolish slavery, others codified it; some made slaves into court eunuchs, others drew eunuchs from the free population, others tried to abolish that institution. And the reason I make such a big excourse into history there is that if there is one pantheon that does constantly change, it's the Shen, most of whom are deified mortals from a wide array of historical eras, who would thus have grown up in wildly different environments regarding such issues. So basically, most of what I can say is: It's complicated.
With Japan, you see even more of that fuzziness. Slavery did exist in Japan for most of the country's history, but weirdly, it did so mostly in name only. It seems as if slavery never was really important in pre-modern Japan, and that the slave population was never very big. I read quite a few works of Japanese historical literature and historical documents, but I've never encountered a single slave therein; I've been told there is evidence, but it's sparse. There were no big slave markets, and more of a kidnapping of certain people by certain other people until yet different people managed to free them or not. Really big was the slave trade the Japanese then held with the Portuguese, but that lasted not even 50 years until Toyotomi Hideyoshi, as part of his general anti-European policy, outlawed it (don't cheer him too much, though, he also robbed peasants of basically all their rights and had lots of Christian converts executed, so ...). Essentially, the attitude of the Kami would be ... they've heard of it, but never held much interest, and gotten off the habit centuries ago.
Beginning with the Portuguese explorations of the 15th century, the Yoruba kingdom of Ijebu, which bought it slaves from the far bigger and more powerful kingdom of Oyo, became one of the biggest exporters of African slaves to the Euro-American sphere. Not only did this extreme demand in slaves permanently change West African culture, intensifying the need for destructive wars to claim new, profitable captives, but it also confronted the sold slaves with a violently different concept of such servitude. People in Africa, in the Yoruba kingdoms, for a long time simply had no idea how much more brutal slavery abroad was, and we have strong historical pointers that they would never have let the trade become this big had they known about it. When word of the conditions in the Americas did reach the homeland through returning freedmen, we can actually see even many prominent slave traders turning into stalwart enemies of their profession, fighting against the ill-treatment of their "merchandise" - look up people like Madam Tinubu.
So if you want to get an idea of how the Orisha view slavery, it may best be expressed as "Yoruba slavery good, other slavery bad". And I think that could be applied to many, if not all cultures. There was slavery in almost every part of the world, at least at some point in history, and the slave owners there probably thought they were doing right. In the 19th century, the Cuban elites railed against British efforts for Abolition as slavery was supposedly the best that could be done for the slaves' salvation, yet derided the Muslim slave trade in the Mediterrannean. Chinese dynasties which were okay with their own slaving system balked at the mutilated and castrated slaves some of their allies sent them as gifts. As I said in the beginning, it's less fruitful to ask how a civilisation sees an abstract concept of "slavery", and more so to ask what it counted as such.