Responses
I think it's probably because in Japan, calling someone by their first name shows a lot of familiarity. So like close friends, family and lovers amongst others. So Ukano probably means it in the terms of calling Sachio dearly.
On the other hand, I feel like the reason why Sachio says Ukano in the translation shows how he wouldn't outright call him babe and such, i think

does anybody know what pet name ukano calls sachio in the og jp version? i'm curious