Tension over what Herbert would say to the endearment gives way to surprise - his hands twitch against his back, then rub little circles there, his voice going a bit softer still.

"...No one? But you're...."

This is still so new, expressing himself like this. He struggles with words at the best of times, and this is...it's hard, even though it's nice. He tightens the embrace a little, wibbling a little before finally settling on a simple statement.

"I'm not going anywhere. I...I think of you as Engel, because you're...you're mine. My guardian."