Valhalla -1

Okabe and Kurisu reunite after a year and a half of separation.

The Distant Valhalla is a Side Story set in the Alpha Attractor Field. It is set 1 year and a half after the Rounder Raid on the lab, and is about "Operation Valhalla", Okabe's plan to escape from SERN captivity. It's a novel, although fan-made anime and Visual Novel has also been made.