Depends on how many hololive idols you plan on.

Fubuki could either be in Northern Scandinavia or Northern Russia.

Kanata somewhere in Italy because angel.

Coco in England or Germany because dragon symbolism.

Towa similar to Kanata (Maybe heresy).

Noel in France or Spain due to religious orders.

Flare could be in any Germanic country due to origins of elves.

Mel in Transylvania and neighbourhood because vampires.

Haato put holy places all over the places because she is HAAAACHAMA-CHAMA.

Matsuri could have holy places in the stereotypically "romantic" cities like Venice, Paris etc. due to Matsuri being lewd.

Marine could be heresy of Matsuri (or reverse) since A) there is no Caribean here B) only lewd remains

Watame can either be in Spain or England, both have history of sheep domestication

Luna could have holy places associated with royal cities mainly around France, because she is princess.

Botan can be South Africa because lion.

Suisei could have holy places tied to cities that have birthed great musicians, one of them could be Wien.

Okayu can be in Egypt due to cat symbolism in ancient egyptian faith.

Korone can be another British Isles faith because she is Cavalier King Charles Spaniel breed of dog.

Mio can be around Greece due to Hatotaurus :D.

Chinese hololive idols should be in Chinese provinces.

Iofi same like Suisei but for artists.

Akirose can either be in Germanic or Greek provinces as she is half-elf, half-siren.

Sora can have holy places in important cities of medieval world (Byzantium, Jerusalem, Rome, Paris etc.) as she is kind of foundation of hololive.

Roboco can be in important industrial places of the world as she is robot.

Rushia can be in Arabia and Jerusalem as medieval necromancy has lot of influences from various Abrahamic faiths (Christianity, Islam and Judaism)

Pekora in Southern France because that is where we get earliest known information about medieval rabbit domestication, alternatively Italy due to Rome and Spain due to Carthage both being involved in rabbit domestication.

Shion can be anywhere in Europe due to her being a witch.

Aqua and Miko, I am not sure.

That sounds good, I'd say aqua and marine could be in important port cities like Bristol or genoa

Trade Republics often hired or sponsored privateers. I could see Marine or Aqua in Venice, Pisa, Genoa, Dardania (Ragusa), etc. Plus with the possibility of Trade Outposts like in CK2, it fits the Ocean-going aesthetic.

Cornwall is know for pirates so a holy site for marine there would make sense. The cornish accent is very similar to the classic pirate accent

I agree about Aqua in the merchant republics of Italy, also because of the red onion.

Aki should be in Germany also since Rosenthal is a German name, specifically Southern Germany since "thal" seems to be used more there.

Noel could be Denmark because of their high consumption of beef. Vikings aren't knights but they're similarly strong like Noel.

Kanata can be in Central Africa because gorilla.

Ayame can be Central Asia/Mongolia because of all the legends from various cultures about demons and beasts there (ergo 百鬼).

Choco should be in Andalus because of all the hospitals and schools there.

Subaru could be in England since baseball originated there and also Peking duck is popular.

Luna is from the Candy Kingdom, and when I think of somewhere with a huge variety in sweets, it's the Middle East, especially Iran.

Lamy doesn't like cold climates despite being a snow elf, so West Africa or India would be good.

Polka could be in Eastern Europe, Middle East, or India since circuses are traditionally associated with the Romani people. Alternatively, she could be in North Africa because that's where fennec foxes are from.

Miko can be anywhere in Western and Central Europe or the Caucasus since that's the range for the wild cherry.

as an idea for Marine, what about the southern sea? Sri lanka, Socotra, Maldives off the top off my head. area was infamous for its piracy.

@bobsimmo Marine is already in places around the mediterranean, its a good idea but its best to keep them concentrated