The Recruit option is comprised by 5 different options (so far), 2 requiring Gems while the other 3 only needs Energy.
The first Energy recruit option (level 1) is unlocked from the start, while the other 2 require a certain criteria to be met before unlocking (second level by beating the 6th Mission in Tokyo level and third one after beating the 9th Mission in the Hong-Kong level)
Known obtainable Warriors per Recruitment Level:
Basic Recruit Level 1:
Basic Recruit Level 2:
Basic Recruit Level 3: