[AERODOG (inu)] PURUPURU NYURUN (Goddess of Victory: Nikke) [English] {Doujins.com} [Digital]

If Rupee ever used "brother" in the official localization, THAT's the actual butchery especially when you take into account how much Rupee takes a liking to the SKK in a romantic (and sexual) way. In context, oppa and onii-chan have multiple meanings in their respective languages compared to the English word "brother", especially if it's a term spoken from a woman to a man. Onii-chan and Oppa, while they are literally words meaning "brother", are used nowadays to refer to guys who the girls look up to and respect and they usually appear mature. Meanwhile in English, if a girl takes a fancy to a boy, she never ever calls him "brother" in an affectionate term. Hence why it was changed to Sweetie.

Pretty sure Rupee called you Oppa or Onii chan in KR while viper called you 자기야 that means babe, darling, honey so it more like EN localization team butcher the translation

Yes. But in their own localization, Rupee refers go SKK as Sweetie and Viper uses Honey

I get the ruby part but Rupee is calling you Onii chan and Viper is calling you darling in JP dub

Ruby? Darling? Onii-chan? The translation is nice but man you can clearly tell these translators did not play Nikke