Demon Lord's Reincarnation

The twenty brave souls that volunteered to undergo Ren's extremely harsh training weren't able to sleep the whole night. They arrived at the entrance of the Northern gates with looks that made it too obvious that they weren't able to sleep. 

Valdel arrived with a group of most of the citizens of the capital city. Those that had jobs like cooking and such had a different schedule from the others. Today was the start of their physical training with Valdel, and they were going to start the day with a morning jog. When Valdel noticed the group Ren was supposed to train he spoke to them.

"You guys should've slept and ate properly before coming here. If Ren truly meant what he said that means you guys are in for something you might not be able to return from... Still, if you guys survive then you might come back as strong as me. Well, anyway good luck." 

After saying his piece Valdel jogged away. The people that came with him looked at the group of twenty with eyes full of pity. 

"Hey, you guys stop gawking at them and follow me. Those that don't keep up will not get to eat!" Hearing what Valdel said the people no longer bothered with the twenty and started running towards Valdel. 

Seeing the fading backs of the others, the twenty who were left looked at them in envy. Just because of a moment of passion they were now in this current predicament. Still, now that they were here and had no way out except for death, they might as well do their best. 

After an hour of waiting in the morning sun, Ren finally arrived with Arthur walking behind him. Ren held nothing at hand, so maybe their morning training was going to be the same as the others like running. That's what they thought and felt a tad relieved. 

When Ren saw the faces of the twenty it was obvious that they hadn't slept nor did they eat. Still, he wasn't going to be kind to them. He then smiled at the twenty which made them instinctively step back. 

"All of you should have slept and eaten while you can. In dangerous situations, you could never know when's the next time you can eat or sleep. Well, since this was your decision to do so, then you need to stick with it. The twenty of you form two straight lines!" 

Hearing Ren's command the twenty immediately formed two lines. It took them a few seconds just to form a line.

"Since this is just day one, I'm going to allow this, but the next time when I say form a line you need to be finished within two seconds. For every second that you delay the more punishment, you shall receive." 

The atmosphere grew extremely tense when Ren said those words. The twenty men and women could practically hear their hearts beating. 

"So before we start our training you would need this." Ren's shadow then grew larger as it surrounded the whole area. From within the Ren's shadow, a set of chainmail, short swords, and sword belts appeared before the twenty. 

"Pick up your equipment and wear them." The twenty quickly moved their bodies and wore their new equipment, while they were doing that Ren summoned a pair of daggers and handed them to Arthur.

"For now you're going to use this as we train." 

"Thank you, master, I will do my best." Arthur took the pair of daggers and nodded his head. Once everyone was properly wearing their equipment, Ren spoke in a loud voice. 

"Alright with your equipment on, we will be running towards the base of that mountain which should be around 20 km, we'll be doing that within an hour. The last one to arrive at the base of the mountain will need to run back and forth two more times. So you better do your best!" 

The twenty were shocked but only a little since they expected something like this, it didn't even sound that hard. As they were getting a bit relaxed Ren spoke. 

"Oh right, while you're running through the forest and the grasslands don't forget about the monsters. On this path, there should be monsters equivalent to C rank adventurers. You either finish them off before continue to run, or you could just outrun them, either way, it's your choice. You guys just need to make it to the base of the mountain within an hour. That's all, begin!" 

The twenty were still stunned for a second as Ren said to begin, but after another second they quickly dashed away. There was no backing out now, it didn't matter what kind of monsters they would face, since the scariest monster of all was the one training them. 

Arthur was also about to begin to run, but Ren stopped him. 

"Your training is going to be a bit different from theirs, so let's head to the mountain right now." Ren picked up Arthur and jumped into the air. 

...

It took Ren two seconds to reach the base of the mountain. Once they were there, Ren looked around. There was a waterfall at the side and a river, seeing that Ren nodded his head. 

'Alright, this is a good place to train. When those guys get near here I'll just guide them towards this place, for now, let's train my little disciple.' 

"Arthur for now I'll teach you the basics of mana flow. Usually, I would teach you how to sense mana by closing your eyes and feeling the flow in your body. But if I do that it would take days before you can sense your mana flowing through your body properly. So we're going to do something different. Hold onto your daggers."

Arthur held onto his daggers as instructed and did a makeshift stance with them. Ren then started gathering some nearby pebbles. 

"You see once you understand the flow of mana you can use that to strengthen your body. Now I'm going to throw these pebbles at you. I'm going to throw them in a speed that you won't be able to match if you aren't able to somehow feel your mana flow and control it to improve your physical ability. It doesn't matter if you dodge it, deflect it, or cut it down. All you need to do is not get hit by the pebbles. Once you're able to not get hit for at least one time, then this training will be over. Now that I think about it, that doesn't sound challenging enough, so let's add a little more. If you're unable to do this task before one of those twenty fools reach here, then you'll stop being my disciple. So are you ready Arthur?" 

Even though Ren gave Arthur a nearly impossible task, the young boy didn't complain, instead, he looked at Ren with even more determination. 

"I will not fail you, master." 

"Now that's what I want to hear. Don't worry, even though this will hurt a lot, it won't kill you. So get ready here comes the first one." Ren threw a pebble at Arthur, who could see it coming but was unable to react on time. The pebble hit him in his abdomen. The force of the hit almost made Arthur puke but he stopped himself from doing so. Ren then continued to fire another pebble at Arthur. 

The next pebble hit Arthur's shoulder which almost made the young boy loosen his grip on his weapon. Yet it did not, it only made Arthur grip his daggers even tighter. Arthur didn't even bother moving for the next couple of pebbles as he took them head-on, as he continued watching them while trying to feel the flow of mana. 

Arthur could somehow sense this so called flow, but he didn't know how to use it to make his body stronger. So he continued to take in pebble after pebble. After a while, Arthur's whole body was full of bruises there were even some small cuts here and there. Yet despite that, Arthur remained standing waiting.

'This kid really does have more guts than most. That look he's giving like he would finish the opponent in one strike is making me excited. Now my little disciple, show me what you've got.'

Ren continued to throw pebble after pebble, and after every five minutes, he increases the speed of the throw just a little bit. It was during the thirty-minute mark when Arthur suddenly moved. His movement wasn't fluent but it was obvious what he was trying to do, he was trying to not dodge the pebble but to strike it down. 

The speed in which Arthur moved was beyond just mere physical ability, he was able to use his mana to enhance his body. Still, Arthur was unable to strike down the pebble. If it was a pebble thrown five minutes earlier then it would've been struck down, but Ren had increased the speed. Even though Arthur had successfully used his mana Ren didn't stop throwing pebbles. 

'I did say until he's able to not get hit.' It took Arthur two more tries before he was able to strike a pebble down. 

"Very good my disciple." Ren approached the badly bruised Arthur and healed him.. "Now that we're done with that, let's move onto the next training."