Prolific
Uncommon10.9%GrindOptionalSingle-player
Have one hundred living dynasty members
Instant: pick any Rurikid ruler in the 1178 start date - the dynasty already has over 100 living members, so it pops the moment you unpause. Doing it organically is a genuine multi-generation project (marry everyone fertilely, no matrilineal matches for the men, keep the kids out of the clergy), but there's no shame in taking the freebie.