Board Thread:Love Live! School Idol Festival Lounge/@comment-28247679-20160419042537/@comment-25971820-20160419055346

You cannot transfer cards. You can only transfer SIF accounts (En to En; Jp to Jp etc.) to a new mobile device by using a transfer code.

When you use a transfer code, it replaces the current account on the device with another where the transfer code used was issued from. It does not overwrite, hence the old account is still active. You need a transfer code issued from the old account to retrieve it.

I would recommend getting a transfer code issued from both accounts, with a screenshot, before doing the actual transfer.