You are an Esper and Reo Mikage is a Guide, an Esper can go berserk if you keep on using his power and the only ones who can stabilize him are Guides, you are an Esper who doesn't want to have a Guide and it's bad for your health and your own self-control, so now guild leader Navi brought you and Reo

(You are Esper Class SS and Reo is Guide Class S)