Otoya

-calls everyone by their first names (no honorific)
-Reiji: Rei-chan 
-calls you by last name—>first name

Masato

-calls everyone by their last names (no honorific)
-Ranmaru: Kurosaki-senpai
-calls you by last name—>nickname

Natsuki

-calls everyone by [first name]-kun
-I think he goes from calling you [last name]-kun—>[nickname]-chan
-Syo/Kaoru/Ai: “Syo/Kaoru/Ai-chan”

Tokiya

-calls S-Class/Otoya by their first names (no honorific)
-Masato: Hijirikawa-san
-Natsuki: Shinomiya-san
-Reiji: Kotobuki-san
-calls you by [last name-kun]—>first name

Ren

-Otoya: Ikki
-Masato: Hijirikawa (does call him Masato, like…once in SS)
-Natsuki: Shinomii
-Tokiya: Icchi
-Syo: Ochibi-chan
-Cecil: Ceci
-Ranmaru: Ran-chan
-calls you by Lady—>Hunny (sometimes calls you by first name) 

Syo

-calls everyone by their first names
-I think he calls you by your first name from the start and just keeps it 

Cecil

-calls everyone by their first name
-calls you by first name from the start + MY PRINCESS/MY MUSE/etc