Haru to Mahou no Kagi

Haruka is a foolish kid that cannot do anything right, and is always helped by her friends. Once, to avoid a group of naughty children, Haru was hiding in the storage locker in the classroom. But it turned out, the locker was connected to another world!! In another world, Haru met Milk, and Leon, a good-looking boy whom she had always seen in her dreams.

(Source: Mnc-comics)