Extreme Cold Era: Shelter Don't Keep Waste - Chapter 19: Scientific Research Commission

Felix's life on Earth had become a series of dead-end jobs, ruined relationships, and rotating apartments smaller than most postage stamps. By all accounts, even his own, he was a coward. Too afraid to move forward, to take risks. Yet when given the chance to choose between risking his life or walking away from a deadly encounter, he didn't hesitate.Moments before his untimely demise, Felix was snatched from earth and thrust into a magical world known only as ‘The Continent’. Empowered by the ‘System,' he learns that he can strengthen himself through combat and dedication. To survive he'll have to push himself beyond his limits, or else fall to the monsters all around him.Levels, stats, and magic. Death is the start of a terrible fate, but if he lives…who knows what he will become.

When an S-class elite assassin-raised captain of a special ops suicide squad comes home from a high-stakes Africa mission, he finds himself offered something that could potentially set him up for life- a curious assignment that he could use to finally exit his days of war and slaughter.

Then placed into a high-school setting, Lin Yi is tasked by the chairman of a top-tier multi-billion company with bodyguard duty for non-other than his own daughter, a certain little Miss of said high-school.

His enemies, once ranging from drug lords, mafia bosses, political figures, and national leaders, are soon replaced with spoiled kids who happen to have rich papas and mamas, and Lin Yi finds his intense expertise and high-threat skillset misused, and very underwhelmed…

But he does get a harem cast as diverse as his old enemies, so Lin Yi decides that, for the sake of messing around with girls as an invincible entity in a down-leveled environment, leaving his bloody and death-filled war days behind is something he’d definitely want to strive for.

- Description from Novelupdates

Dr Dalton Wyatt, a world renowned Scientist and Inventor is transmigrated to the body of a high school student Dalton Wyatt who committed suicide due to unfortunate circumstances and complicated life.

Jacob Steve, an Old Man, died at 116 after living a whole life.

But Jacob always had a dark side, which he always suppressed and hid from others.
However, in the later years of his life, when death was inevitable, he understood there wasn't any point in having wealth, knowledge, or desires if you couldn't have a life to enjoy them.

He became obsessed with fabled immortality and devoted his reaming life to extending his fleeting lifespan, but just like any other failed.

However, he mysteriously got another chance at life and found a way that led to fabled immortality.
But he was also forewarned that the way led to it was filled with blood and darkness!

In the end, Jacob chose it anyway with no way of going back, and it was also the start of his suffering and his icky, brutal journey toward the 'Immortality' he wanted so badly!