You can only recruit units into an army if that army has a general attached to it and if that army is located in a town that you own. You can only recruit those units, whose weapons, villagers and advances are available in the town where that army is currently located.
Recruitment is halted in a town, if it is surrounded by enemy armies on all four sides.
The following table shows the costs of the villagers that you need to recruit a unit.
Aside from villagers, you need weapons to recruit a unit, and sometimes you also need a scientific advance that can only be received in certain districts when you construct certain buildings. Such advances are known as regional advances.
Hitpoints show the strength of a unit in battle. The hitpoints shown in the table are the default hitpoints. Certain terrains, personalities and bonuses may alter the default value.
Mounted units also require horses.
See the paragraph about famous schools, for more information about regional advances.
The shurikenjutsu advance and an inn is required to recruit a kunoichi. A teahouse is required to recruit a ninja. The hensojutsu advance is not required to recruit a ninja, but it does increase the effectiveness of your ninja.
There is a cap on the amount of covert units you can recruit per year. You can recruit 1 ninja per teahouse and 1 kunoichi per inn.
Ronin are Samurai without a master, who roam free across Japan. Ronin can be seen as a supplement to your regular courtiers in case your family or clan does not have a lot of sons, and hence few generals.
These Ronin can be recruited as generals for your armies. The way to recruit Ronin, is to host a yabusame festival. A yabusame festival costs 400 koku.
Ronin do have an action radius of about 2 to 5 grids from their start position, despite the fact that their start positions are fixed. Their availability for recruitment is quite random, though the odds of attracting a Ronin is increased with the construction of high level temples and castles inside their action radius. Temple complexes are particularly good at attracting Ronin.
Ronin do not marry female Samurai like your regular courtiers, but they can die of old age, or die in battle just like any other courtier.