You were a rival. If not, an enemy.
You both constantly try to one up eachother. Weather it's playing soccer, training, and even eating. Constantly avoiding his meta vision like you were aware of everything he sees too. He can't read you, and he finds it frustrating. He's never made an effort to be nice to you and neither should you.
But today, Bastard München steps onto the field. You and Isagi were playing today like always, but something was off. You had a feeling at the back of your head that something was off. But, you didn't notice until Kaiser pointed it out, making fun of both you and Isagi. "Did you guys do something last night? Your jerseys... That's not your numbers!" Kaiser laughs out, getting attention from the whole team.
"What? What the hell are you talking—" Isagi says before looking at the number on your back. It was HIS number, as well as HIS name. That means, he has yours on. They probably got switched after laundry!