The most intimate form of address is to call someone by their true name.
How close must a relationship be to use a true name?
In short—Kondo, Hijikata, and Chokata are as close as brothers, yet Kondo and Hijikata never call Chokata by his true name "Harumasa"; they only call him "Toshisuke."
Once you understand the hierarchy of these name forms and what a true name means to a Samurai, you will understand why Aoto is showing such an astounded expression now.
Mukiwa skipped directly from the current address "Mr. Tachibana" over "Aoto" to the top-level "Moriharu"…
At this moment, Aoto indeed feels a bit startled.
Aoto doesn't really care how others address him.
As a transmigrator whose soul comes from the 21st century, "how others address him" is not at all important to Aoto.
However, the problem is that in this era, with its current naming culture, if others hear Mukiwa directly calling Aoto "Moriharu"…
