At the beginning you will have only 10 Akaris buy you can get more Akaris until 50 solving the different Akaris.

Akaris	How to unlock
Akaris 11 to 20	Solve 5 of 10 akaris.
Akaris 21 to 30	Solve 10 of 20 akaris.
Akaris 31 to 40	Solve 15 of 30 akaris.
Akaris 41 to 50	Solve 20 of 40 akaris.