I was confused about that part. Sachio Shinobu? Isn't it supposed to be Sachio Ukano? Or Ukano Sachio, I guess, since this is Japanese. Or am I wrong and Ukano and Kurumizawa are not family names? I swear they sound like family names...
They are family names! Sachio's full name is Kurumizawa Sachio (胡桃沢・さちお) if they got married he'd automatically take Ukano's surname so his name would be Ukano Sachio (宇迦野・さちお)
Also a cute detail in the Kurumizawa and Ukano families' naming traditions is that every member of the Kurumizawa family has their names written in hiragana (which is usually only used for women's names because it sounds too cute :') ) and everyone in the Ukano family has single character names (忍-Shinobu 社-father 巽-brother) which comes off as more formal (and a little intimidating but that might be me lol)
I feel like the renta TL team dug themselves into a corner with certain things,, saying ukano is his given name and making him talk rather casually with sachio will all make the chapters after this harder to translate...
Ukano's name is shinobu (given name-忍) ukano (surname-宇迦野) his brother and father are also surnamed ukano and they refer to him with his first name (shinobu)
Ukano also pretty much always uses keigo(敬語-polite speech) with sachio, I get why they chose to make him call sachio "babe" (and tbh i kinda like it) it'll cause problems when sachio asks him why he always uses polite speech with him,,,i feel kinda sorry for whoever is going to have to fix all this