FAIR WARNING, POTENTIAL SPOILERS WILL FOLLOW.

ef Honorific Usage
(or Why We Kick Ass at Translating)

For the vast majority of the cast we went with our standard stance, which is to drop honorifics unless being directly addressed. This helps cut down clunky-sounding English without losing some implied meaning in situations that really call for it. Besides that, the cast in the first two chapters are all a rather informal bunch, so the removal outside of direct address tended to mean very little.

We decided to make exceptions for certain characters. Chihiro was the big one. Her memory is more or less locked into the mindset of a little girl due to her accident at a young age. This is made apparent during one of her first meetings with Renji:

Chihiro: "Let's see... Is "Renji-san" okay with you?"
Renji: "'-san' is too formal. Why not '-kun'?"
Chihiro: "That's too much for me."
Renji: "I'm younger than you."
Chihiro: "That's true, but why do names suddenly matter?"
Renji: "Well, in any case, we're friends."
Chihiro: "Hm... I understand. Let's see, then. From now on I'll call you Renji-kun."

Essentially, she's stuck in the mindset of a polite little girl who isn't comfortable with dropping honorifics. She has to be convinced to change Renji's honorific to a less formal one. That's why we decided she would be the only character to keep them at all times.

Mizuki has one big exception but otherwise follows the standard ruleset. We decided she would keep the -sempai honorific at all times because role models are important to her. When she meets Chihiro, she makes this quite clear:

Mizuki: "Chihiro-sa... Ah, if it's okay with you, could I call you Chihiro-sempai?"
Chihiro: "Huh?"
Mizuki: "Well~, you're older than me just like Kei-sempai, so it feels weird to call you differently, ahahaha."
Chihiro: "Is that so? Well then, let's be sempai and kouhai."
Mizuki: "Yay~"

Mizuki has a bit of an obsession with being able to call people with the -sempai honorific as you can see.

The one other thing of note is using Mr. and Ms./Mrs. before adult character names. This should really be self-explanatory, but in English, would you ever call friends your own age "Miss" or "Mister"? Keeping those as honorifics (or just dropping them) sounds a lot more natural. On the other hand, changing them to Ms. and Mr. for adults is perfectly normal and flows quite well.

Thank you for your understanding!