[Tachibana]

Spoiler for 57:

Thats another thing that is evident to Issa being controlled, why would he subjugate himself to someone like the Masked King? He is the leader of the most powerful family of vampires in the world, by taking order from someone like the Masked King and who isn't a vampire, it would bring down both his reputation and pride as a vampire, and thats definitely something Issa himself wouldn't like and it would also make him look like a weakened figure to other vampires.

Either Gyokuro or the Masked King can be doing it. IMO, I think it's Gyokuro doing it, think about it, she knows that she won't escape the Masked King's wrath should she fail, by controlling Alucard she can overthrow him and take the world for herself and plus if Issa was being manipulated by the Masked King, and if he were to discover this, than he would use Issa to take out Gyokuro.