Reincarnated in DXD(rewrite)

Two days have passed since I brought Katsumi home, and tensions have been running high ever since. While my parents accepted Katsumi's presence without issue, they couldn't overlook the reckless way I had returned—teleporting out of the underworld without any prior notification or authorization. To them, this wasn't just a violation of protocol but a breach of trust and a blatant disregard for the laws governing magical travel. In the underworld, teleporting between worlds without government approval or a special permit from the Four Satans is considered illegal entry, a serious offense that could result in heavy penalties. Due to strict regulations, travel between realms typically requires the use of specialized vehicular modes of transportation, such as the interdimensional trains that link various worlds. The only exceptions to this rule are the faction leaders, such as the Four Satan's or individuals who they have been granted explicit permission. My parents made it clear that my actions had not only jeopardized my safety but could have caused Political issues or worse.

As a result, I faced my mother's wrath—a terrifying experience to say the least. The memory remains crystal clear: me kneeling in a dogeza position, trembling slightly as my mother loomed over me, her expression deceptively calm yet menacing, with faint traces of the power of destruction radiating ominously from her form. Her voice was icy but firm as she delivered my punishment. First, she cut off my financial support, leaving me to pay the considerable fines for illegal teleportation out of my own pocket—a blow that stung deeply given my reliance on that money for projects. Second, and perhaps worse, she banned me from entering my lab for two whole months. Knowing my obsession with my experiments, she had chosen the punishment with surgical precision. I could only sit there, enduring her silent glare, knowing that any protest would invite an even harsher fate. That moment taught me one thing—my mother was not someone to be trifled with, and she knew exactly how to strike where it hurt the most.

For these two agonizing months, I must find ways to keep my sanity. Every day feels like a battle against the constant flow of new ideas swirling in my mind—concepts and experiments begging to be realized in the lab. It's maddening, but the fear of my mother's wrath keeps me in check. I know that defying her would only result in harsher consequences, so I focus my energy on planning future projects and honing my theoretical knowledge, biding my time until the ban is lifted.

Gremory Garden

"Yum yum! Ice cream!" chirped a small white creature happily, its voice high-pitched and cheerful as it eagerly devoured a cone of chocolate chip ice cream. The warm afternoon sun cast dappled light through the leaves of the towering tree under which it sat, creating a serene backdrop. Nearby, a young boy with vibrant crimson hair stood beside a gray-haired girl, both appearing calm yet attentive, as if waiting for something to begin. The creature licked the ice cream with an air of contentment, its little legs swinging back and forth as it watched the pair curiously, completely oblivious to the training session about to unfold.

"Today, I'll teach you about mana control, an essential skill for becoming stronger in the future," I began, addressing them with a calm yet authoritative tone. Katsumi glanced at me, her brows furrowed in determination. "Is this going to be as difficult as that endurance training, we did last week?" she asked, her voice laced with both curiosity and wariness.

"Endurance training is different," I say with a slight smile, hoping to ease her tension. "That focused on building your physical stamina and pushing your limits. This training, however, is all about precision and finesse. Without precise mana control, even the most powerful spells can become unstable, backfire, or waste precious energy. In combat, efficiency can be the difference between victory and defeat, and proper regulation of mana output ensures that you're never caught off guard or drained too quickly." I give her a reassuring nod. "Think of it this way: while strength is important, control is what makes that strength truly effective."

I paused for a moment, letting the importance of my words sink in. Katsumi's gaze didn't waver. "It may look simple," I continued, "but mastering this exercise will serve as the foundation for more advanced mana techniques. So, pay close attention."

Demonstrating, I placed my right foot on the tree trunk, followed by my left, and began walking vertically up the tree as if it were flat ground. I moved effortlessly, without using my hands for support.

"The Tree Climbing Practice trains you to control your mana by focusing a fixed amount at the soles of your feet. If your mana flow is too weak, you'll lose your footing and fall. If it's too strong, you'll be pushed away from the tree, potentially damaging it."

Just as I finished my explanation, two familiar voices called out.

"Hey Maxius! What are you and Katsumi doing? How are you standing on the tree like that?" Rias, my crimson-haired sister, and Akeno, with her raven-black hair, approached us curiously.

"I'm training Katsumi in mana control," I replied, repeating the explanation I had just given.

"I want to try it! What about you, Akeno? Doesn't this Tree Climbing Practice sound fun?"

"It does sound interesting," Akeno admitted, a spark of curiosity in her eyes.

Having them join wasn't a problem. In fact, their presence created a healthy sense of competition that motivated Katsumi to improve faster. Kei and I watched from the shade as the three girls repeatedly fell on their backsides, much to our amusement.

What I hadn't anticipated was Rias informing our mother and the rest of the family about our training. This piqued their curiosity, and soon enough, a crowd of family members gathered to join in. My parents tried out the exercise and mastered it in just two days—expected, given their centuries of experience with mana control. The real prodigies, however, were my brother and sister-in-law, who both grasped the technique within minutes, showcasing their exceptional control.

Unexpectedly, my brother saw tremendous potential in the exercise and, ever the strategist, began promoting it throughout the underworld as a revolutionary method for devils to improve their mana control. Without delay, he contacted influential figures and spread word of the technique's effectiveness. It didn't take long before interest surged, with various devil factions eager to adopt the practice. Before I fully grasped what was happening, the Tree Climbing Practice had become one of the most popular and widely used training methods across the underworld, praised for its simplicity and practicality.

To my surprise, even elite warriors and scholars sought to learn the exercise, hailing it as a breakthrough in mana refinement. My brother's influence ensured that this training not only spread rapidly but also gained the recognition of the Four Satan's themselves, who endorsed it as an official training regimen.

The tree climbing practice lasted two intense weeks, filled with countless falls, laughter, and moments of frustration. By the end of it, Rias, Akeno, Katsumi, and even Sona—who had joined a few days after the others—had not only learned to climb but had mastered the technique to such an extent that they could leap effortlessly from tree to tree using only the soles of their feet. Their progress was remarkable, a testament to their perseverance and growing mana control. Each of them, despite initial struggles, displayed unique flair in how they approached the exercise, adding a personal touch to their newly acquired skill.

"Congratulations on completing Level 1 of mana control training!" I announced.

"Level 1?" Katsumi repeatedly disbelief.

"So, all of that was just the first level?" Rias asked incredulously.

"There's more?" Akeno added wide-eyed.

"How many more levels are there?" Sona questioned, intrigued.

"Before I tell you, you need to promise not to share this with anyone—not even Mom and Dad."

"What? Why? They're family!"

"Well, if you don't want to learn, that's fine by me."

"Alright, fine. I promise."

"Good. Now, Level 2 involves walking on water by coating the soles of your feet with mana"

"What?"

"How is that even possible without using a spell or a magic circle?"

"Follow me and I'll show you."

We made our way to the lake on the castle grounds, the sunlight glinting off the water's surface in a dazzling display. Without hesitation, I stepped forward, placing one foot onto the water's surface and letting my mana flow steadily through the soles of my feet. I took another step, walking across the water as though it were solid ground. The surface rippled gently beneath me but held firm. The girls stared in awe, their eyes wide with astonishment and curiosity, as though trying to decipher the trick behind what I had just done.

"I turned back to face them, a small smile playing on my lips as I gestured for them to step forward, confidence brimming in my stance. "Alright, now it's your turn. Don't be afraid; just focus your mana and trust yourself."

"Amazing!" they exclaimed in unison, their voices ringing out with a mix of awe and excitement. Katsumi's eyes sparkled with determination, while Sona adjusted her glasses, already mentally dissecting the process. Rias folded her arms, masking her intrigue with a competitive glare, and Akeno's face lit up with genuine wonder. The moment was filled with anticipation as they prepared themselves to take on the challenge, each one eager to succeed and outdo the others.

I returned to dry land, brushing a few stray droplets from my sleeves as I addressed them once more. "This method is significantly more challenging than the Tree Climbing Practice," I explained, my tone serious. "Unlike climbing trees, where the mana output remains relatively stable, water walking demands constant adjustment. The amount of mana you emit needs to change dynamically with every step to counteract the water's shifting surface tension. If you emit too little mana, you'll sink. Emit too much, and you'll disturb the surface too violently and lose balance." I paused, watching their expressions shift from awe to apprehension.

"It may seem impossible at first," I added, offering a reassuring smile. "But once you learn to synchronize your mana flow with the natural movement of the water, it becomes second nature. Now, it's your turn to give it a shot. Stay focused, stay calm, and most importantly…don't panic when you start sinking."

Thirty minutes later…

Plop!

Plop!

Plop!

One by one, they sank like stones. Kei, sitting beside me under the shade, laughed heartily. "They keep sinking like rocks!"

I couldn't help but laugh too, the sight of Rias splashing into the water over and over again providing a sense of comedic satisfaction. It wasn't just about her falling; it was about all those little moments in the past when she had picked fights with me, only for me to finally enjoy a small victory. Perhaps my younger age was indeed influencing my personality, making me more reckless and playful than usual. Still, seeing her determination as she got up after each fall, ready to try again despite the repeated failures, earned my silent respect. Even in the midst of playful rivalry, I couldn't deny her persistence. It made the entire exercise more enjoyable and, truthfully, brought a sense of camaraderie to our training.

It took three weeks, but eventually, they all mastered water walking. Sona was the first to succeed, followed by Katsumi, Akeno, and lastly Rias, who didn't take kindly to being the last, given her competitive nature.

Though I had developed more advanced levels of mana control training, I chose to hold off on teaching them further for now. Rias, Akeno, and Sona primarily fought as wizards, relying on ranged spells and strategic casting rather than close combat. Therefore, additional mana control training focused on physical combat wasn't immediately essential for them. However, I made a mental note to revisit this decision in the future, as their growth might eventually benefit from mastering more advanced techniques.

"Alright, that concludes our training."

"That's it?" they asked, clearly disappointed.

"Yes, and now that we're done, Katsumi and I have other training to attend to."

"Hey, Maxius, we want to keep training too!"

"No can do. Katsumi's training is tailored specifically for her needs and abilities. She's working on techniques that wouldn't necessarily benefit you right now," I explained, noting their crestfallen expressions.

"But if you're serious about improving, here." Reaching into my magical storage, I pulled out several neatly bound books, each shimmering faintly with an enchanted cover. I handed them a copy of the elemental clone technique, one of the most versatile methods I had come across. "These books will guide you on creating elemental clones. It's an advanced but invaluable skill. Clones can serve as distractions, scouts, or even backup in battle if used creatively. Focus on mastering the core principles, and don't rush the process. Proper execution is key."

They accepted the books eagerly, their disappointment giving way to renewed enthusiasm. Seeing their determination, I added with a grin, "Remember, each element reacts differently when forming clones, so you'll need to adapt your approach based on your affinity. Good luck."

With that, Katsumi and I took our leave, heading toward the dense woods where we usually trained in solitude. Knowing Rias, she probably wouldn't take the clone technique seriously; after all, forming clones from destruction magic would be an incredibly complex task. Still, part of me wondered if her competitive streak might push her to at least experiment with the method. Akeno and Sona, on the other hand, had natural elemental affinities—lightning and water, respectively—which gave them a solid advantage. I could already imagine Akeno perfecting lightning clones to enhance her offensive capabilities, while Sona might develop clones that could manipulate water to trap or disorient enemies.

I hoped they would stick with the training long enough to see its true potential. The elemental clone technique wasn't just about creating replicas; it was about strategy, adaptability, and using one's environment to gain an upper hand. As Katsumi and I moved further into the woods, I felt a sense of quiet satisfaction, knowing that in some way, I had just planted seeds of growth that could one day reshape how they approached combat.

For the remainder of my punishment, I dedicated myself fully to Katsumi's training, focusing on developing her physical endurance and refining her combat skills. Each morning began with intense conditioning exercises designed to push her stamina to new limits—running through the dense woods, scaling rocky inclines, and performing repetitive strength drills. Afterward, we shifted to martial arts, where I introduced her to the fundamentals of aura—or touki, as it's called here—a technique that enhances physical abilities by channeling internal energy.

Once she grasped the basics, I moved on to more advanced combat forms, teaching her jujutsu for grappling and close-quarters techniques, and hakuda for swift, powerful strikes. We sparred tirelessly from morning until night, our movements echoing through the forest, accompanied by the rustling of leaves and the occasional calls of distant wildlife.

In addition to physical combat, I taught her the basics of instant movement—known in some worlds as flash step—a high-speed technique that, when mastered, allows one to move faster than the eye can follow. We practiced repeatedly, focusing on short bursts of speed to build muscle memory and precision. Over time, her movements became quicker, more fluid, and far more unpredictable, signaling significant progress.

Despite the exhaustion we both felt at the end of each day, I could see the fire of determination in Katsumi's eyes growing brighter. By the end of those two grueling months, she had transformed into a more resilient and formidable fighter. Though I was still grounded from my lab, the sense of accomplishment I felt from seeing her growth made the punishment worthwhile.

By the end of those two months, Katsumi had grown remarkably stronger, and despite being grounded from my lab, I felt a sense of accomplishment seeing her progress.