To connect to the game you need to have a DMM account. You can register under the English side, but switch to Japanese language after logging in. You will also need to enter a region flag cookie if you're outside of japan. If you don't then you'll get the area error page.
Cookie code
document.cookie = "cklg=welcome;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/"; document.cookie = "cklg=welcome;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/netgame/"; document.cookie = "cklg=welcome;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/netgame_s/"; document.cookie = "ckcy=1;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/"; document.cookie = "ckcy=1;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/netgame/"; document.cookie = "ckcy=1;expires=Sun, 09 Feb 2019 09:00:09 GMT;domain=.dmm.com;path=/netgame_s/";
Once you have the code copied, you need to open your browsers developer console, paste the code, and press enter.
Chrome: Ctrl-Shift-J (Windows), Cmd-Opt-J (Mac) Firefox: Ctrl-Shift-K (Windows), Cmd-Opt-K (Mac) Safari: Cmd-Opt-C (Mac) Opera: Ctrl-Shift-I, Select 'Console' (Windows)
Finally you can go to the game. Direct game link http://www.dmm.com/netgame/social/-/gadgets/=/app_id=463129/