Toaru Majutsu no Index SS - Volume 2, Chapter 7: Someone Behind the Scenes is Unprepared and has to Clean Up. The Second Friday of May.

In a dark space secluded from the rest of the known galaxy, a young man wakes up in a struggle for his life.During his coming of age ritual, it was revealed that he possessed the heavy soul body, A talent that could potentially rival even the gods. Joy overtook his entire household as they prepared for the eventual rise of their clan.But on that same day, the Hand of judgement fell upon them extinguishing all traces of life on their planet leaving it as a dead world…As for him? Fate had other plans. Cast into the darkest and most secluded place in the known universe, The sanctuary, he is faced with a decision, become stronger and survive or wallow in misery and Die![You have Awakened ][ Hidden Class Unlocked : SSS Soul King— Supremacy over all Souls and soul kin ][ Innate Skill unlocked: Heavy soul brilliance— In the following 20 seconds host will become effectively Unkillable]-—WSA Entry-—

During this revolution era book, Fang Ru was the original heroine of the cannon fodder. She died in repression and infamy under the deliberate calculations of the transmigrated heroine.

After being reborn, Fang Ru decided to stay away from the leading male character and start over. However, without Fang Ru’s involvement…

The leading male character became crippled and turned evil. He suffered mutual torment, mistreatment and hatred with the new female protagonist, who also lost her chance at love and career.

The lovelorn supporting male character was forced to live like a widower for the rest of his life after being manipulated into marriage by someone with a rich family background, even still he harbored feelings for someone else’s wife.

- Description from Novelupdates

This novel is also known as Deep Ocean Survival: A Submarine From The Start

The whole people traveled through, and everyone was trapped in the ocean abyss two thousand meters below the alien ice layer!

There is only one basic pioneer ship at the start!

Food, oxygen, water pressure…
Unpredictable seabed turbulence…
The powerful and terrifying Abyss Siren…
Evil and mysterious parasitic flora…

With all kinds of potential threats that follow everywhere, this road to survival is doomed to be extremely difficult!

However, when everyone was desperate for the hardships of survival, Meng Lei was calm and composed.

Because he found that he could actually see the system prompt!

“At a distance of 500 meters, a shipwreck of an alien pioneer was found, and the supplies inside are enough to make you rich!”

“At a distance of 1200 meters, I found a doomsday worm, rush up and kill it, and you will become the brightest cub wandering in the dark abyss!”

“The distance is 4,500 meters, and the ruins of an alien civilization are found. The danger level is SSS! Why are you standing still, turn around and run!”

- Description from novelbuddy

The strongest Demon Lord dies, and reincarnates as a human. Not only that, he because of various incidents turns into the hero’s best friend.

Follow his journey as he tries to help the hero escape his fate, and on the sideline to conquer the continent while he’s at it.