back number is a lifestyle app developed by Fanplus Inc. for Android devices. The app is free to download and is designed for fans of the Japanese rock band back number.

The app provides the latest news about the band and exclusive content for members of their official fan club, "one room". You can enjoy various types of content such as movies and member blogs. The app is easy to navigate and provides a seamless user experience. With back number, fans can stay up-to-date with the latest activities of the band and enjoy exclusive content that is not available anywhere else.