User blog comment:B214/Volume 21 info & spoilers/@comment-95.90.224.210-20160602194640/@comment-1359322-20160603031840

Sorry but i don't understand your complain about how Ise acts in front of Millicas cause it's only natural that Ise acts in a humble way towards Millicas. Millicas is a noble and of higher status than him. Not only is he the son of a Maou, he's the nephew of their master even if Ise is Rias' boyfriend, it doesn't change the fact that Rias is still his master and Ise is still a servant. It's the same as how Ise has to show respect to Rias' parents. Besides, it's not just Ise, all of Rias' servants are acts in the same manner it's not just Ise, even Irina who's unrelated to the Gremory team shows certain amount of respect to Millicas.

"“Even an Angel like me is really keen to hear it, despite being nervous!”

Xenovia and Irina fixed their posture, which is a rare thing, as they were waiting for the words of the boy with crimson hair."

So i don't see the meaning to complaining how Ise acts in front of Millicas cause that's not a matter of being humble, it's a matter of respect. He's merely respecting Millicas who's part of Rias' family, the Gremory clan.