If there would be around 200 canon nation characters in a Hetalia completed cast and each country could be shipped with every single one of them, regardless of circumstances, there would be around at least 80,000 possible ships (counting self-cest and nyo!talias but not duplicates like north or south, the micronations and other non-nation character).
Snake demon au needed more characters so here’s Arthur! There’s lots of missing people about because of Yao and Arthur’s a vigilante obsessed with catching him, but of course he always slips away. They have a little history together involving a one night stand where Arthur ended up falling for him but Yao was like “Lol no” and… yeah. Hurt feelings. uvu)/