It's not really cop and thief game. It's a pact which the council made for takara because if they didn't do it would be chaotic inside the school, but someone broke the pact rule and so everyone thought 'if someone broke the rule then so can we because that would be unfair' so they chased takara.
Kashiwagi called it cop and robbers game, so takara wouldn't suspect anything and mine-chan kissing takara infront of the whole school has the same meaning as 'i caught the thief' so the so called game end.
So takara is the thief and the whole school body is the cops
Soo that chapter when they have a pact cop chasing the thief. Can someone explain itu to me? Who is the cop and the thief?