The Lord of the game, along with some of his retainers (i.e. Avatar Character), are training along the country side. Bandits come in, easy victory ensues, a messenger comes along tells the Lord something happened at the capital, Lord rushes onward...
...to multiple battles with Bandits and eventually his own country's Soldiers leading to them discovering a coup for the throne. Unfortunately the coup succeeds, the King is dead, the Lord is framed.
The Lord escapes, travels around the neighboring countries slowly gaining troops and aid from other rulers. The Lord charges for the capital, the Avatar dies protecting the Lord.
The Lord becomes king of a country who believes him to be a mad man thirsting for power, rebellions happen.
Epilogue: The instability of the nation causes it to burn from the inside leaving to the very nations that aided the now King taking land as their own.
Maybe a part 2 about how the descendants trying to restore said country years, if not decades later. This is just to add child units who have some story significance that doesn't involved multiverse.
Also skinship greatly affects which nations will aid you.