Rainbow Days manga may have come to an end, but a new side-story manga will be launched by Minami Mizuno. The announcement was made in the April issue of Shueisha's Bessatsu Margaret magazine, while the release of the new manga will begin on July 13 in the August issue. However, the serialization schedule will be irregular.

Mizuno launched Rainbow Days manga in February 2012 in Bessatsu Margaret, which ended with the last chapter in the April issue. The manga inspired a television anime series, which premiered in January 2016.

Source: animenewsnetwork.com