Limited-offer Super Managers are only available in the Shop for a certain amount of time, and they cannot be obtained from Common/Rare/Epic Briefcases like other Super Managers.
When a limited-offer is available, you will see a special Briefcase in the Shop which shows the name of the limited-offer Super Manager.
You need to collect Special Tokens in order to open these special Briefcases. If you do not use your collected Special Tokens before the limited-offer expires, you will permanently lose those Special Tokens!
If you use your Special Tokens to open special Briefcases before the end of the offer, you will permanently keep the Fragments which come from those Briefcases.