If a fighter had chosen to become a wizard, he probably wouldn't develop a high enough strength attribute to become a paladin later on. With some non-human classes, the change is not something to choose. Wyrms become wyverns once they have the appropriate abilities, for example. One of my golems became a stone golem when it was petrified by a cockatrice's attack. Soldiers are actually three separate little guys with spears who fortunately take up only one slot in one of your units.
Soldiers are special due to their importance to a legion, but more on that later.
I have stated that Ogrebattle 64 works with an entirely distinct set of game mechanics, but thus far we have yet to reach the bulk of what makes it so different. The game focuses quite a bit on military, and on strategic use of an army. Your army is composed of units, which are composed of characters. A unit must be led by an eligible leader. On any given mission, there is a limit to how many units you may deploy.