Log in method Icarus M provided are [Google account login], [Facebook account login] and [Guest Login]. [Google and Facebook accounts] is to login using accounts you have been used. [Guest Login] is not using Google and Facebook accounts but log-in with information in device. [Guest Login] may cause loss of account’s game data by deleting the app and changing device etc. so if you want to secure your account, please use log-in of [Google and Facebook accounts]
Unfortunately, if you forget your guest login information cannot be restored at any chaces. if you log-in using guest account because of [linking accounts] function on the in-game setting after the log-in, please use the function via the setting menu before enjoying the game.