In dragon ball you can invite more battle crew to assist on your journey , but first you have to upgrade this rank system. click on your main character picture on top left corner, you can see your current fame and receive your daily salary.
Daily Salaries is given, well, daily and it consists of Silvers and Potential Points. You can claim it after reset on 00.00 and AFTER your Fame Rank increase
Once you get enough prestige, you can raise your fame rank. Higher fame will give you more stat bonus, better daily salary, and ability to bring & recruit more crew (MAX battle crew is 5 crew).
To upgrade this rank system you just can get from daily arena reward and attack the other player ( Lose - 100 fame , Win - 200 fame )
There is a step tittle to get max battle crew , these here are the steps :
♦ 3 Crew
For first time you can battle with 3 crew from martial ( Martial trainee to trainee celestial )
♦ 4 Crew
Then after upgrade the rank to elite turtle you can invite 1 more crew to your formation
♦ 5 Crew
To upgrade max battle crew is take a long time , you have to reach rank to Master - turtle