East Asia total war set during the 1200s would seriously be a good title. There’s a lot of parallels that can be drawn to Rome 2’s factions.
Southern Song Dynasty = Macedon
Taking Sino/Chinese culture as the equivalent to the Hellenic/Greek culture.
Jurchen Jin Dynasty = Parthia
Cavalry dominant, but can eventually field decent infantry.
Mongols = Saka/Sauromatae/Scythia
Horse archer spam incarnate. Alternatively may also be seen as Rome because they’re the “winners"
Western Xia/Tanguts = Seleucids
While it’s a mishmash of Chinese and Tangut/Steppe culture, but more Chinese. Seleucids are an Eastern-Hellenic hybrid, but more Hellenic.
Western Liao/Kara Khitan = Pontus
Chinese and Steppe culture mishmash, but more Steppe. Pontus is an Eastern-Hellenic hybrid but more Eastern.
Tibet = Armenia
Mountain kingdom, some of the heaviest cavalry of the Far East second to the Jin Dynasty (Armenian vs Parthian Cataphracts) but limited.
Genpei Japan = Epirus/Illyrians/Odrysian Kingdom/Dacians
Epirus because some Chinese influence, Illyrians because of as wako pirates raiding the lands to their west, and Odrysian because of their obsession with 2-handed polearms such as the naginata, which is like the Thracians with their rhomphaia. Dacians because their yumi bows aren’t that bad, but not stellar. Same can be said of the Dacians’ horse archery and foot archers. Also falxes.
Goryeo Kingdom = Bosphoran Kingdom
Located in the north, Chinese-influenced. Tends to get invaded by northern nomads. The Chinese once said that the Koreans had the best foot archers.
Southeast Asians = Celtics and Germanics and Iberian barbars
They’re relatively lighter in equipment, utilize javelins and falcata-like swords, and lack siege equipment and navies.
Dai Viet = Massilia
Southeast Asian faction with Chinese cultural influence.
Dali Kingdom = Colchis
Chinese-like mountain faction, but generally fields light troops