The Keiichi thing?

No, naruse is the family name so ichika's name should be naruse ichika/naruse keiichi, between ichika/keiichi, one of them might be a nickname. Naruse's first name.... hmmm I think it hasn't been mentioned... naruse and asumi are still not on first-name basis yet..

IT WAS MENTIONED Mr. Naruse’s full name is Keiichi Naruse/Naruse Keiichi. I saw it in kne of the chapters yesterday but I can’t recall which chapter. You can google his name it has tons of results https://myanimelist.net/character/167176/Keiichi_Naruse

First name basis is used when you're very close to each other. Using it to address the person older than you is disrespectful. So this should be ichika not keiichi.

Keiichi is the family name of Mr. Naruse. Read the sypnosis here to see it: https://myanimelist.net/anime/38797/Papa_datte_Shitai

And I don’t know how it works in Japan but they call him “Mr.” Naruse, doesn’t sound disrespectful to me.

The translation one I mean, daiki keep saying keiichi when it should be ichika.

As you said he’s not close to the child so he uses the child’s family name

Nope, it is Naruse if you saw the original Japanese. it is written in the family plate: 成瀬 (Naruse) then 壱佳 (Ichika) and 圭壱(Keiichi)

That's what I am trying to point out, it should be 'Ichika' not Keiichi. 'Coz Keiichi is Mr. Naruse's first name.

If you see the characters below keiichi is supposed to be naruse's firt name and ichika's full name is naruse ichika. Trust me naruse is a common surname in japan. Tho I don't understand how could daiki call naruse by his first name unless it's a translation error. It's not disrespectful to call someone by their family name+san (which probably translated to mr.) it's the polite way to address someone.

Oops I misread I thought you said it's disrespectful

I think Naruse is the last name. Naruse was written on the door on the first chapter.
The names on the last chapter though, so confusing.