Some useful bookmarklets which may or may not still work.
Visit page in device emulation mode (Chrome dev tools)
javascript:(function() { function set(name, value) { document.querySelector('[name='+name+']').value = value }; set('nickname', "InsertNameHere"); set('subject_password', 'InsertPasswordHere'); set('subject_password_for_confirmation', 'InsertPasswordHere'); set('year', '1969'); set('month', '4'); set('day', '20'); document.querySelector('[for="receive_mail_magazine"]').click() }());
http://game.granbluefantasy.jp
javascript:(function() { var page = parseInt(window.location.href.split('/').slice(-1).pop()); window.location.href = window.location.href.replace(page, page+1) }());
http://game.granbluefantasy.jp/#serialcode
After using the bookmarklet below, you may have to click each input individually, and manually type something (anything) to get the button to be enabled.
Serial code 1
javascript:(function() { 'j5pa mkru 2vcx 4cr8'.split(' ').forEach(function(x, i) { document.querySelector('[name=alphanumeric'+ (i+1) + ']').value = x; }) }());
Serial code 2
javascript:(function() { 'yrwg yv8m cck2 wcbf'.split(' ').forEach(function(x, i) { document.querySelector('[name=alphanumeric'+ (i+1) + ']').value = x; }) }());