Yumemi ga Oka Wonderland

Kotarou is a middle-school boy living a mundane life without dreams. His only distraction is to chat with a lively high-school girl he calls "Miss Akogi", who plays the guitar in the street. After a UFO suddenly crashes in the middle of the city, the world around them starts changing in unexpected ways. Suddenly, everything seems possible… (Source: MU) Note: Chapter count includes two extras