This one got easy with the new Mass Conversion feature in Holy Fury. Here are the steps I used to get the achievement:
You can use the same steps #1 - #6 to convert to Catholicism (instead select the King of Italy as your sponsor in step #7) or Orthodox (just select the Byzantine Emperor in step #7). I didn't see this approach mentioned in the wiki, so I passing it along for anyone who may be interested.
EXTRA CREDIT - you can also use steps #1 - #6 to work on the Holy Smoke achievement. Since Capua is adjacent to Rome, instead of making a Mass Conversion, you can swear fealty to the Pope.
Once he accepts you as a vassal, then use the Intrigue Focus to spy on the Pope, and wait for the imprison event to pop. Once he is in your dungeon, you can sacrifice him in a Great Blot. You have a lot more troops than him, so he usually gives you lots of titles. It was nice seeing a legendary Viking Reaver like Fairhair as the Designated Regent and Chancellor of the Papacy.
- Start as Harald Fairhair, Duke of Ostlandet in Norway, 867 start
- Declare Coastal County Conquest on the Count of Capua in Southern Italy.
- Sail your armies to Capua, and siege it down.
- You start the game with 400 prestige, so once you win this war, you will have 500+ prestige.
- Request council support from your councilors.
- Once a majority agree to support you, raise Tribal Organization to Low, then to Medium. Raising it to Low doesn't count as a law change, so you don't need to wait to go to Medium.
- Go to your religion tab, click the Mass Conversion, and pick the Sunni King of Africa as your conversion sponsor.
- Wait a few days for him to accept, then BOOM- your capital county immediately converts to Sunni religion.
You can use the same steps #1 - #6 to convert to Catholicism (instead select the King of Italy as your sponsor in step #7) or Orthodox (just select the Byzantine Emperor in step #7). I didn't see this approach mentioned in the wiki, so I passing it along for anyone who may be interested.
EXTRA CREDIT - you can also use steps #1 - #6 to work on the Holy Smoke achievement. Since Capua is adjacent to Rome, instead of making a Mass Conversion, you can swear fealty to the Pope.
Once he accepts you as a vassal, then use the Intrigue Focus to spy on the Pope, and wait for the imprison event to pop. Once he is in your dungeon, you can sacrifice him in a Great Blot. You have a lot more troops than him, so he usually gives you lots of titles. It was nice seeing a legendary Viking Reaver like Fairhair as the Designated Regent and Chancellor of the Papacy.