Wouldn't an exciting adventure be one where the PCs have to retrieve one of Arrusif's pieces from pirates who stole it from the harbor before it could be unloaded into Almantha? A pirate crew of Water and Air Mages would be a great challenge to overcome...or infiltrate.
Alright, so he has to physically build the Devices he needs to manipulate the Nexi in such a way as to take control of the Sun. It's like Tesla's Device from The Prestige (good movie, go watch it, I'll wait).ehhh... Let's say "magitechnical". Blood magic per se doesn't really exist, but the devices he uses in the climactic ritual are designed to interact with nexi in a magical way.