Shi found Hyousuke and Daisan in the courtyard with the soldiers. "Hey, you're gonna need to whip these guys into shape within the next few months. I may have started a war." Shi said, walking up to them. "What?" Daisan and Hyousuke exclaimed simultaneously.
"Don't worry, they don't take us seriously so they'll probably just send a couple thousand soldiers and some mages to crush us." Shi said casually. "How is there nothing to worry about? That's more than our 500 or so men can handle." Daisan asked. "It's fine because they were stupid enough to warn us before attacking. We need to give them a lesson in overconfidence." Shi said, heading to the walls.
Shi arrived at the walls, and headed outside of the castle. He found a large area of land that the incoming army would have to head through to reach the front gates and started hollowing out the earth under it, leaving threads of rock to hold it up solidly, but having the threads converge in one place.
That done, Shi formed the ground of the pit into large spikes, leaving only the area by the convergence point of the strands spike-free. The whole process of making the trap took all day and left Shi exhausted and drained.
Shi marveled at how different each core level was. He would've been drained not even a quarter of the way through at green core, and he wouldn't have been able to even attempt the trap at yellow core.
Shi went back to the castle and went straight to his room to sleep. He awoke after a couple of days and went straight to the kitchens for food and water. Shi realized he needed to pace himself or else he'd just waste valuable time.
Shi left the kitchen and went to the battlements. When he got there, he inspected the wall, the wall alternated between being waist-high and being taller than a full-grown man, allowing archers to take cover in between shots.
Shi went back to the castle and got a crossbow from the armory. After returning to the battlements, Shi levitated himself with wind magic to the same height as the average soldier and aimed the crossbow out at the woods.
Shi used earth magic to raise the wall to a level where he could set the crossbow on it for stability at the perfect height for an average soldier. He then raised all of the aiming sections of the wall to that height.
After getting the height set, Shi used earth magic to bring another section of the wall about a foot above the part of the wall used for aiming. This created a foot tall slit in the wall, allowing the soldiers to be relatively safe while aiming their crossbows with more accuracy than they usually would have been able to because of the added stability of resting it against the bottom of the slit.
Shi went out into the forest, using his mana sense to search for a large mana source. He eventually found one and sprinted towards it, finding a bear with fiery red fur and large, dark teeth. Shi drained the bear of its mana while dodging its clumsy attacks, leaving a wrinkly bearskin behind him as he returned to the castle.
Shi used the mana he got from the bear to start working on the ramparts. After a week of off and on work on the ramparts, Shi finished them. He went and found Daisan, who was training the crossbowmen in the courtyard.
"Daisan, I set something up on the ramparts, get the men used to shooting with their crossbows braced against the ramparts. They need to be able to shoot a fly's dick off at 40 yards in a few months."
Daisan nodded and started getting his men set up on the ramparts, where they set themselves up. Shi saw Daisan setting up targets outside the gate as Shi went out into the woods.
Shi used mana sense to track another magical beast. He came upon a giant wolf, with black fur that had red streaks through it that looked similar to lightning bolts. Shi activated stoneskin and walked towards it.
Shi had realized that something was wrong the first time he used the ability, he wasn't sure if it was his lack of understanding, or if it was the ability itself. Shi used his mana sense on the stoneskin as he let the wolf attack him.
The wolf's attacks bounced off Shi without any impact felt by him. Shi saw the mana that encompassed his body in a shell stay completely still. Shi frowned and made another layer of stoneskin around his hand under the layer he was using around his body.
Shi activated war cry and punched the ground hard. There was a loud boom as trees were uprooted and the ground around him seemed to raise up. Most importantly, Shi saw the outer layer of stoneskin shatter, with the inner layer having cracks running through it.
Shi stood up and looked around for the wolf, only to see it lying dead a few feet to his right. Apparently, the shockwave from his punch had killed it. Shi searched for another magical beast to test his new theory out on.
Shi eventually found another one of the red bears and tried a different version of stoneskin. He made a barrier right around his skin identical to the earlier one, but made an outer layer that was thicker, and more flexible.
The bear charged Shi, but could do nothing to him as its paws bounced off Shi like he was made of rubber. Shi activated war cry and punched the ground again, but this time, the barrier persisted.
Shi stepped out of the crater he had made and headed back to the castle. Shi went straight to his room and started moving his mana around. Shi practiced controlling his mana precisely, making it wisp around, or dart to each corner of the room. Shi also practiced changing the mana's form, making it thinner or thicker, soft or hard, or making it visible to normal people and nearly invisible to himself.
Shi practiced this with the dedication of a blacksmith, only leaving his room for food and water. After a few months, Daisan knocked on his door. "Come in, Shi called." Making his mana cycle through all the colors of the rainbow. Daisan entered, "They'll be here in a day." He said a bit nervously.
Shi stood up, "Let's go welcome our new guests then." He said, walking out of the room, smiling.