Upvote:2
Per TIMATIC, an Indonesian citizen needs a visa unless they hold a visa for certain other countries1, Japan not included. To obtain a toursim visa (probably B2), the person trying to visit should contact the nearest South Korean embassy.
1 Australia, Austria, Belgium, Canada, Cyprus, Czech Rep., Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland (Rep.), Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, New Zealand, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, USA or United Kingdom