Fired up Crusader Kings III.
Started as Alfonso VI of León, in a relationship with my own sister *insert anime meme here*
Promptly got married to an eligible woman and seduced another courtier.
Murdered my brother in Galicia, my brother in Castille inherited his territory, putting me in a territorial sandwich.
Declared war on Aragon, my brother in Castille declared war on me while my army was away *Surprised Pikachu*
Somehow my brother loses the war and retreats, despite having more than double my troops *Blinking Guy Drew Scanlon*
Sister's husband discovers and reveals our incetious secret. Wife forces me to leave my relationship with my sister *Picard Facepalm*
Patch up my relationship with my wife.
Murder sister's husband with no complications.
Seduce my sister for one last beautiful night together before assuming a traditional sibling relationship.
Murder my annoying brother in Castille, inherit his territories.
Ready to conquer and unite Spain in the name of free love for all!

10/10, was worth cashing out some of my CS:GO items to buy it.

UPDATE:
Start conquering the rest of Spain, progress is steady.
While seducing a courtier, my sister walks in on us, and I invite her to a threesome, after which she (again) and the courtier become my lovers.
Defeat massive peasant uprising.
Sister dies, leaving me low on allies.
I die, my infant bastard son inherits the throne.
All my vassals declare war on me in favor of placing some obscure cousin on the throne.
I lose the war, game over.

Still 10/10, this is my Game of the Year, since Cyberpunk isn't out yet as of 12/1/2020.