I made a Japanese Civilisation Concept last year and I plan to rework it once I tested the new Civilisations.
Now they are adding a civilisation that only has one generic unit (the Archer) and at last 5 unique units.
One idea could be splitting the Japanese units into Ashigaru (Simple foot soldiers), Samurai (Knights/Elite units) and Sohei (Warrior Monks) that are each trained in a different building.