@givemersspls that's a good point. Actually we bought Japanese raws and thus used Japanese translation for this webtoon because we couldn't acquire the Korean raws (can't purchase Korean raws unless you have a Korean number).
Working with Japanese manga regularly, the word onsen didn't particularly stand out to me. But I can see how it can be kind of jarring from a reader point of view. We tried our best to keep things consistent in the Japanese TL but I guess I missed that.