Prepared resume documents (English CV, Japanese CV and Japanese work history sheet) prior to the interview and handed them over upon arrival.
First a short written test which covered IPv4 subnetting, TCP/UDP port numbers, Linux commands and a few general questions on servers and LDAP/AD. The questions were in Japanese but there was no need to actually write Japanese. The test was not difficult and I scored almost full marks.
After that began the main interview with 3 engineers. It was entirely in Japanese, quite technical but also relaxed, and I enjoyed it very much. It took a bit longer than expected which I thought was a good sign. They asked general questions like what are your main responsibilities at work, was the hardest issue you had been troubleshooting etc.
A few days after the interview I was notified that they rejected my application. The reason given was that while they liked my network and Linux experience, they want someone with more middleware skills. Which surprised me a bit since middleware was neither part of the job description, nor the written test and was only shortly discussed during the interview.
Nevertheless it was an overall good experience.