As of today, Closers Online is, um, closed in Japan. SEGA has shut down the game’s servers and is handing all operations of the title over to Taiwan’s HappyTuk, which is starting the MMO back up on its own hardware.
Fortunately for those affected, Japanese players can migrate their accounts and progress to the new servers and continue to play using their native language. A new client will need to be downloaded and installed, as the old one will no longer work after the change of guard.
No reason was given for the transfer between publishers.