Though imo the cultural usage in LiL is always trivial (I mean, Kumon-mi is literally a place in Japan using American customary units and currency), I could prove that at least in China and Japan honorific for teachers is always Surname-Teacher as name is always written in case of Surname-Name on the contrary to that of English, because Chinese is my mother tongue.
This way the name of Sekai could be spelled as Arakawa Sekai with maiden name unknown. I remember father of Kanda Sisters once mentioned Sekai abandoned her maiden name due to the terrible relationship with her family. I won't deny possibility of that opening with letter T despite being weird for her to tell that personally to Akira and it seems that it's an unspoken rule that all the characters in LiL has name and surname begin with same letter (with exception of Arakawa Nozomu and Yuu).
I just think we won't get a clear conclusion here nevertheless.
You're right, it's usually name-honorific in many languages. However, you can drop the name and call someone of higher status simply by honorific, but you absolutely can't drop the honorific and just use someone's name in most cases like a teacher. And you are still that honorific independent of your name if you earn it (e.g. you
are 'Sensei.') But again, English is title-name, so it would be Teacher-Name, and it doesn't really work the same in English anyway. I'd ask for more insight for Chinese specifically, but that may go even more off topic. Anyway, I think you're right and that the cultural stuff might not always be correct or really important.*
I feel like I remember a line in which someone says something along the lines of "Isn't it weird that we use [American thing]" although I can't actually remember. But I would say that most cases of this come down to the game being in English, written by an English speaker, and for English speakers largely, so everything is sort of "auto-translated" for us, beyond basic things like Yen. So while the setting is Japan, the author is just gonna write dollar or pound or yard or freedom. That's the lazy explanation at least. Also yeah we're not getting any clear answers to a lot of shit for a long time.
If you think this is desperate, just wait until we get into the letter A discourse.
A is for anal, it was foreshadowing the Maki event where Akira almost had his penis removed.