MTL - After Time Travel, I Married the Heroine and Her Brother - Chapter 84

Side story of Kyoukai Senjou no Horizon bundled with the first press release of the 1st, 3rd, 5th and 7th Blu-ray volumes of both seasons of anime.

This side story follows Asama, Kimi and Mitotsudaira aboard Musashi one year before the beginning of the main story, as Asama is considering to create a music band together with her two friends for the next festival in Aki, a territory under the governance of K.P.A. Italia.

One day, Luo Jian woke up from his sleep and found himself in a locked chamber where the door and window were all sealed. A note with a few lines written on it was tacked to the wall: “Escape from this room within an hour, otherwise, you will die.”

There is a sequel called Reincarnation Night (轮回之夜) that takes place in the same universe but has different main characters

- Description from Novelupdates

In a world ravaged by radiation and the remnants of war, Dylan is far from a classic hero. A lieutenant with a tainted past, he's just trying to survive the ruins of a dying world... until the day he wakes up bound and surrounded by the mutilated corpses of his comrades.Captured by monstrous creatures, he soon realizes he’s been transported to another world. A world far more dangerous, far more brutal—where only the strong survive, and even monsters are hunted. Saved in extremis by Maggie, his commanding officer, he begins a desperate escape. Their only hope may lie in their encounter with Élisa, an elf abandoned by her kin, and their discovery of a mysterious power: anima gems—stones imbued with spiritual essence that can enhance body and soul, and unlock the path to awakening.No One under 18 admitted

Due to a bug in the game, Ren Changsheng accidentally left the game idle for ten million years.As he watched the endless stream of experience points, all Ren Changsheng could think was, 'I really do not want to level up!'