Miklagarðaríki

Needs Northern Lords; start and stay North Germanic Ásatrú (no ruler-designer characters), control ALL of Thessalonika's counties, and hold any empire title that is NOT Byzantium. As Hæsteinn (867): first, a quick conquest war on Napoli purely to get in diplomatic range of Byzantium (hire mercs, ransom nobles). Then Invade Kingdom on Thessalonika, ideally while the empire is distracted - siege inside the war goal and force strait crossings for the field battles. For the empire title, the wiki suggests the delightfully obscure Empire of Ajuraan (only 18 counties, reachable via Naqis while dodging the Tulunids). Once it pops, the wiki's follow-on is Frankokratia: capital to France, convert culture and faith, second achievement free.