Steins;Gate: Mugen Enten no Arc Light

The manga, based on 2010 drama CD, tells the story of what Mayuri experiences during the final chapter of the visual novel (anime episode 23) and the lives of Mayuri, Okabe, Daru, Suzuha, and Ruka in the year after Okabe's first failed attempt to save Kurisu in the 1.129848% β world line divergence.

(Source: Steins;Gate Wikia)