Meitantei Shikkaku na Kanojo

There is a boarding high school. Konoha meets a girl on the entrance ceremony day. Her name is Karen and she suddenly says to Konoha, "You're the culprit." According to her, the mysterious thief who sent theft notice to the school the other day is Konoha. She doesn't know what's going on, but Karen believes that Konoha is the culprit.
(Source: HimeyaShop)