Seikaisuru Kado: Aoi Haru to Railgun (正解するカド 青い春とレールガン, eng. Kado - The Right Answer: Blue Spring and Railgun) is a manga that takes place immediately after the end of episode five of the anime series, and tells another story untold. The official release date was May 06, 2017.
The story was published on the "Comic Zenyon" website, the digital outlet associated with North Star Pictures and Tokuma Shoten's Monthly Comic Zenon seinen manga magazine. It features artwork by Kouki Ochiai.
The manga follows a pair of high school students whose lives are completely changed after the arrival of the Kado cube and the unlimited energy source Wam.