the event descions series of the shogun, try to break away from men trying to control. a weak of but diplomatic shogun, to damyio he trust he out his seal of authority, for damyioo/clan leader gain it title of offices, that give boost in honor, rentuie cap, and easier to recruit ronin. For shogun after said amount of time can formal ask to swear loyalty as faithful retainer, possible gaining a powerful vassal.
If shogun weak there possible of strong lord coming in, with high rank court, to use the poor shogun as a rubber stamp. Now thing control of shogun similar the pope control in CK, he call crusades well shogun can name clan enemy of the state, which affect would be ever clan dog pilling who ever is the enemy of the state, and high chances of non member of ruling family of clan to break away.
If puppet/weak shogun can break of away from de facto master, use ability him self.
If reasonably strong lord take the Kyoto, depend on bloodline and trait he as different option, if claim to have relation to the Seiwa Genji line(he gain this through family, marriage, or just forge it.), then gain all ability of the shogun with out having master over his head. Or can install himself as the Protector of Kyoto ( that would name for defacto master of shogun/ruler at court, or install himself as regent if his court title is high enough.
Final level of shogun would be strong, (by game mechanics normal some get declare shogun.) Time period in game of how they stay together will repersentive the time period of shogun consolidation of his power over Japan.