Valkyries Calling - Chapter 3: The Son of Ullr Returns

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

The world had started doomsday, and I struggled for a year, before I died under an enchanted beast’s claw. Heaven has given me another chance, back a day before the end happen. Will I be able to change my fate, and that of my loved ones? Now, I will start my journey on becoming the strongest on the planet that the Gods have changed into a game world.