UPDATE: Sega has acknowledged the issue and are investigating it. They don't currently have an ETA on when the servers will be up.
UPDATE 2: Sega has officially classified it as Emergency Maintenance. It appears that a failure with the server equipment caused the issue. They don't currently have an ETA for maintenance completion, but they are considering providing compensation for the downtime.
UPDATE 3: Sega has said that the emergency maintenance will force the rescheduling of the 2:00 JST ARKS League and the 7:00 JST Magisterial Onslaught. They will be rescheduled for a later date. They're sorry for the inconvience and ask that we remain patient and calm while they work on the server.
UPDATE 4: Sega says that they hope to have the servers online by 10:00 JST.
UPDATE 5: Servers are back online!
Many people (both JP and non-JP players) have begun reporting issues with the servers not allowing them to login, move to different ships/rooms, and disconnecting them at random. SEGA has not announced anything at this time, and the cause of the issues is unknown. We'll update this post with more information as it becomes available.
To re-iterate: This is happening to both JP and non-JP players.