Burning Bright in the Forests of the Night

Shingeki no Kyojin: Nubatama no Yoru no Mori ni, Akaaka to Moyuru (進撃の巨人　ぬばたまの夜の森に、あかあかと燃ゆる) is a visual novel. It was released on December 18th, 2013 in Japan and bundled with sixth anime Blu-ray.