Since you mashed up a bunch of eras together, What era did you want me to research for japan?
General officers and the King himself are mounted on elephants They are often depicted as directing and ordering their subordinates. Spears and bow and arrows are commonly unleashed from this position. It has an advatage of elevation and it give the troops the extended reach needed.
Khmer warriors wore little or no body armor at all. This give them the advantage of speed and agility, but offer no protection to the body, limbs, and head.
Spears and shields are the two main weapons an infantryman carries. It is used in the same manner as other warriors during that era, but tactic wise (Europeans), I'm not sure.
The last and most effective weapon of all is the individual soldier himself. Khmer warriors were rigorously trained in Bokator (today's prodal serey)and wrestling. It arguably the most effective martial art used for hand to hand combat, ancient or modern.
Also, Khmer warriors thought tattoos where where good luck and protected them, and they where as valued by soldiers in khmer like chainmail and plate was in the west.
Ive read from a few sources that the khmer kings and officers where called Brahmin, Although i know that they are traditionally priests in the Hindu caste system, so i have no idea how much merit that holds.
Nayar or Nair it mean SERPENT in Sanskrit
1603. — "The men of war which the King of Calicut and all other kings have is Nair... each being a gentleman... their women be of great beauty and rare to catch sight of... possessing fine neat features... befitting the noble class" — John Kanding
"...On the west coast there are a few curious distinctions that indicate, apparently, difference in racial origin. The first of these instances is that of the Nair, the military caste of Malabar. Their traditions point to the north as their native land; they are light in colour, in very great contrast to the rest of the castes of the tract, have retained the custom of polyandry, with a good deal of serpent worship. It appears that they advanced upon their present tract by way of the coast higher up, but how they got there does not appear. As with the Arya, they found a dark race in possession and enslaved them on their estates, where they labour to the present day. In the same tract, too, there is a class of Bráhmans, the Nambudiri, of remarkable fairness of complexion, and noted for their rigid ceremonial puritanism. Then, again, in the track of the Nair's alleged progress, we find a peculiar caste of Brahmans, partly occupied in the cultivation of spices and betel nut, but settled mostly above the Gháts, and not therefore so well sheltered from foreign influences as the Nair, who sought the coast. These Havig or Haiga Bráhmans show their connection with the Túlu country in their speech, and, like the Nairs, attribute to their caste a serpent origin in Rohilkhand, a statement borne out by their title. Between these we have a class of female temple servants of an equally light complexion amidst a universally dark population.."(Jervoise Athelstane Baines (1893), General report on the Census of India, 1891, London, Her Majesty's Stationery Office, p. 184) ?
"Before quitting the country (Kerala) Hyder Ali Khan by a solemn edict declared the Nairs deprived of all (social and political) privileges and (ordered) not to carry arms. This ordinance was found to make the submission of the proud Nairs absolutely impossible because they would have thought death preferable to such humiliations and degradation. Therefore, Hyder Ali Khan by another ordinance, consented to restore all social and political privileges including carrying of arms, to the Nairs who embraced the Mohammadan religion. Many nobles had to embrace Islam; but a significantly large section (Nairs, Chieftains and Brahmins) chose rather to take refuge in the kingdom of Travancore in the South than to submit to the last ordinance" — Prince Ghulam Muhammad of Mysore
"The Nairs of Malabar who attained much celebrity in warfare....justly entitled born soldiers...by the virtue of their descent they must always bear arms..they constitute the third and the last of the honoured castes....a privilaged people....the Rajahs like the oriental monarchs are fond of exaggerating their importance and boast of the number of Nairs they have in their country and service to impress us (the Portuguese) with the idea of their wealth and power" — The Book, Letters from Malabar
I found a really cool genealogy book on the Dynasties of the Khmer, If you need names for lords, i can give you a few names.
Also that hooked Club thingy in the 3rd from the last picture looks wicked