Kai had slumped down on the floor and was panting heavily. If the small boulder took him that long, how long would it take for him to lift those large boulders? A strengthened body could possibly lift those large boulders but in three times the gravity, it was impossible. Gravity was not as simple as it seemed. A body that was twice as strong could endure twice as much, that was true. But it isn't the same for gravity.

No matter how strong the body, four times gravity would definitely hinder the blood flow. Of course, Kai knew that Reo would put some precautions so he wouldn't die, but that doesn't change the fact that he would face six times the gravity soon.

Kai stood up after much effort and walked back to the small boulder, he had pushed it as much as he can toward the other side before Reo had appeared.

"The third hour has come, I will now increase the gravity."

Kai slammed down into the floor instead of kneeling, the increase was too much for his legs that were already tired from four times the gravity. His body was still a seven year old's after all, his bones had not finished strengthening, and his muscles were still soft.

"Damn it!"

Kai grit his teeth and punched the floor.

"Then, I'll just have to adapt!"

Kai closed his eyes as he made his body relax. After two hours, Kai began to stand up.

"Haa... haa..."

He was panting as he stood up and began to place his hands on the rock.

"Haa!"

Kai pushed the rock a bit and it began to move.

"Haa!"

Kai once more shouted as he pushed the rock.

"I can do this!"

Veins were appearing on Kai's body as he used [Body Enhancement] to the absolute limit.

"Haa!"

Kai pushed the rock with even more force than before, before he knew it; the hour had ended. Kai was in the pit for a total of six hours now.

Kai's legs became jelly when the small boulder had finally reached the other side.

"Haa... I'm going to the other side now..."

Kai was hallucinating while seeing a bright light as he stared up to the sky, needless to say it was the sun; he was really hallucinating now, thinking that the sun was the passage to the other world.

"Haa... looks like his body can only withstand this much."

Reo had a disappointed look as he retrieved the orb and Kai's unconscious body.

Reo flew to the cave and placed Kai's body near the fire and let him rest.

After at least half a day, Kai had woken up.

"Ugh..."

Kai sat up and held his head but his body was also aching all over.

"Wh...ere am I?"

"Oh you're awake."

Reo was floating in front of Kai as Reo laughed.

"Looks like the pressure was too much that you started hallucinating and now you don't even know where you are."

"Ah."

Kai suddenly paused and made a sound of realization. His face suddenly turned furious and tried to punch Reo but unfortunately for Kai, Reo was a spirit that couldn't be touched physically.

"Agh!"

Kai yelled as he retracted his hand backwards, Reo had gotten through unscathed but Kai's tired body had gave him pain when he tried to use his muscles to punch Reo.

"Calm down... Just because I threw you in a pit with more gravity than you can handle and not give you any food for six hours, doesn't mean you can just punch me..."

A case of literary theft: this tale is not rightfully on Amazon; if you see it, report the violation.

Reo innocently told Kai his deeds which made Kai's eye twitch but he managed to hold himself back because of the pain. Kai fell silent and looked down.

"Reo."

Kai's voice became serious.

"What is it?"

"Teach me a body technique that's more effective than [Body Enhancement]."

"I can't."

Kai drooped down but immediately asked.

"Why?"

"Because, I'm a spirit. I don't know much about body techniques."

"You've got a point but you have a millienia's worth of knowledge inside your head don't you?

"Yeah, but there's absolutely nothing here."

Kai drooped down but his guess had hit the mark. Reo was definitely hiding some body techniques but only because he wanted Kai to be independent.

"Then it can't be helped."

Kai ate some food and stood up as he closed his eyes.

"I have to adapt."

Kai breathed in and out slowly.

"The human body can adapt to two to three times Earth's gravity, judging by the pull of the gravity on this world I found out through magic; the gravitational pull is only slightly stronger than that of Earth's. That means humans in this world have certainly adapted to gravity of this much, then I just have to do the same, only faster."

Kai smiled and began to gather his magic. He added pressure to himself and the surroundings.

"Four times."

Pressure pushed down Kai and his surroundings, he was trying to replicate the feeling of four times the gravity but it wasn't possible.

"Agh!"

Kai coughed up some blood and fell down.

"My body..."

"Are you an idiot...?"

Reo's eyes had shock in them though it wasn't because Kai had coughed up some blood.

"Why did you just try to increase gravity while injured?"

"You've got a point there..."

Kai weakly acknowledged Reo's words.

"Then, I'll just...go rest..."

Since Kai had coughed up some blood, he was a bit pale and his body was weak. He drifted into sleep but as he feared, he had been woken up at midnight and dragged into the pit once more.

Kai sat down and didn't lift any of the rocks, he closed his eyes and tried to adapt to the gravity.

"Adapt... adapt... adapt...!"

Kai repeated his words like a chant, on the day that he did so, he had lasted twice as much as before; twelve hours!

He repeated the cycle of sitting down and adapting to the gravity day after day. Unknowingly, two and a half months had passed and Kai could finally move freely in twenty times the gravity. Although lifting rocks still required effort, Kai had progressed very much and Reo could see his growth.

In the span of two and a half, Kai had transferred all the small boulders and half of the large boulders. He was now enthusiastically lifting large boulders at four times the gravity. His [Body Enhancement] mastery had increased by a lot and it wouldn't be an exaggeration to say that he was one of the best in the country. After all, not everybody in this country could experience gravity.

"I'll definitely clear this today."

Kai made a grin and lifted the large boulders, it was midnight as Kai finally got all the boulders to the other side. His body was toned and his height increased, his face hadn't changed a bit since three months ago but the air around him changed.

"Amazing, you exceeded my expectations. I had thought you would've needed two years."

"Two years? Isn't that a bit too long?"

Kai tilted his head for a bit but when he thought about the day he first met increased gravity, he nodded his head.

"Thanks to the gravity, I actually thought about new magic and new ways to fight."

Kai had a grin on his face as he bragged.

"I'll give you three days of rest since you completed it in two and half months.

"Eh?"

Kai was taken aback by Reo.

"Three days?! Isn't that a bit too short?!"

Kai tried to change Reo's mind but unfortunately, he hadn't succeeded.

"Nope, in fact, the next training will be even more severe. Remember Kai, this is all so your body can withstand my spirit magic."

Kai sighed dejectedly but Reo had a point, power just wouldn't fall on his lap.

"Fine."

Kai scratched his head and began to find food. He had been seldom eating for the past three months because he had only ate once a day at midnight. 

Kai secured a boar to eat and ate inside the cave.

After that, Kai had stepped out of the cave once more and stretched his body.

"Time to test my body."

Kai channeled [Body Enhancement] and sprinted, his speed was nearly a lot faster than that of before, he was running so fast that he knew that if he ran back to his clan, it would take him three hours. He could cover the distance of walking for a few days in three hours, that was a significant feat.  

Kai was shocked by his speed and ran through the forest for half an hour before he instantaneously kicked the floor and sprinted back, he was a bit slower than before but he was definitely still very fast.

"Amazing..."

Kai ran quite the distance but wasn't tired in the least. If a normal person were to run at full speed for ten minutes, they would be out of breath for a minute or two, but Kai wasn't like that at all. He had used [Body Enhancement] on top of his already strengthened body but that was still quite hard to do.

Kai moved towards a nearby tree and used [Body Enhancement] once more. His right fist shot out and the tree trunk had a huge dent.

"Now, the moment of truth."

Kai closed his eyes and darkness began to spread across his body.

[Body Enhancement] used mana to coat the body and strengthen it from inside and outside. His mana had been trained to the point that it could withstand twenty times the gravity with [Body Enhancement]. But, just how strong was his magic power now?

"[Shadow Ball]."

Kai's calm voice resounded throughout the forest and a ball of darkness shot out from his palm to the nearby trees. It hit the first tree and immediately exploded, it wasn't an explosion made of bombs, it was an explosion of the darkness attribute. Black smoke spread throughout the blast range and every tree within were turned black and all destroyed, they were separated from the tree trunks easily.

"Amazing..."

Kai repeated his previous words because he could not contain his praise.

"If anyone were to be hit by my full power, I doubt they can carelessly just let it hit!"

Kai grinned and roared into the sky.

 "I'm a step closer to my goal, I'll definitely surpass you!"

Kai vowed once more to who knows where but only Kai knew, he was vowing to the one that reincarnated him.