MTL - This Is My Primitive Tribe - Chapter 1 scary jungle

Gu Zuo: Are you sick?

Gongyi Tianheng: You have medicine?

Gu Zuo: You’re sick!

Gongyi Tianheng: If I say I’m sick, can you cure me?

Gu Zuo: If I say I have medicine, would you want it?

Gongyi Tianheng: However much you have is how much I want.

Gu Zuo: However much you want is how much I have.

Gongyi Tianheng: Then bring it all out.

Gu Zuo: …

Simply speaking, a scaredy-cat shou transmigrated and had to think of a way to survive. He had a golden finger called Medicine Refining System, but unfortunately, he didn’t have the ingredients needed to refine medicine and level up.

A great young master to an Empire’s preeminent Clan had a super high IQ, but his talent for cultivation was low. Unfortunately, pill refiners were too hard to develop, and weren’t restricted to his personal service. But he could acquire plenty of ingredients.

Two people, one was sick and one had medicine. Therefore, the one who was sick kept the one who had medicine, and everyone was happy.

- Description from novelupdates

The course of commitments never did run smooth.

What happens when a scientist from a futuristic world reincarnates in a World of Magic and Knights? An awesome MC is what happens! A scientist’s goal is to explore the secrets of the universe, and this is exactly what Leylin sets out to do when he is reincarnated. Dark, cold and calculating, he makes use of all his resources as he sets off on his adventures to meet his goal. Face? Who needs that… Hmmm… that guy seems too powerful for me to take on now… I better keep a low profile for now. You want me to help you? Sure… but what benefit can I get out of it? Nothing? Bye. Hmmm… that guy looks like he might cause me problems in the future. Should I let him off for now and let him grow into someone that can threaten me….. Nahhh. *kill*-

Alternative: Leylin is transported from an advanced technological era into a medieval world— except there’s magic. Equipped with “only” his quick wits and an A.I. chip fused to his soul, he sets out to become the most powerful magus the world has ever known. In a land divided into the Light and Dark Magi, the weak can either be cattle or disposable slaves. Only the strong can determine their lives, and only they have the luxury for virtue. Yet strength is only a tool for Leylin, like any other. His goal, in the end, is his own.

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!