Mushoku Tensei with gacha system

Two months had passed since my last duel with Eris. In that time, I had worked tirelessly, not only with her but also to regain my mana reserves for another spin of the gacha. The gacha system requires a large amount a mana to spin so it took me 2 months to gather enough for another spin. The first spin had granted me Gwen Tennyson's ability to create magical constructs—a power that had already proven invaluable in the duel and is the reason why I got my job. But now, it was time for another spin.

The gacha system materialized before me again, the familiar wheel spinning in the void. My heart raced as the symbols blurred past. I watched it slow, praying for something useful—something that could help me, especially with my struggles teaching Eris.

The wheel came to a stop. A soft chime echoed, and a new power revealed itself:

Knowledge on Bounded Fields – Medea.

Medea. The name rang a bell, bringing memories of reading about her in novels and games and a very popular anime. She was a prodigy from the "Fate" series, an ancient Greek sorceress who transcended all magical expectations. She wasn't just any mage; she was a genius, feared and revered for her magical prowess.

In the Holy Grail War of Fate/stay night, Medea had cracked the summoning system in a week—a system that should have taken centuries to master. She summoned a fake Assassin by manipulating the rules, and her use of bounded fields was legendary. These fields could defend against nearly any attack, warp reality itself, and bend the laws of space and time. To have even a fragment of her knowledge… it was a godsend.

My body tingled with the rush of newfound knowledge. It wasn't just magic anymore—it was a deeper understanding of magical theory. I felt it sink into my very bones, unlocking new possibilities. The complexity and structure of Medea's bounded fields opened a world of tactical, defensive, and offensive options. For a moment, I was overwhelmed, but I smiled.

This would change everything.

I stood in the courtyard, stretching my fingers, letting the mana flow through me with a newfound clarity. Eris watched from a distance, her arms crossed impatiently.

"You've been standing there for an hour," she said, her tone half-exasperated, half-curious. "What are you doing?"

I smiled, turning toward her. "I've been… thinking."

"Thinking?"

"About magic. About how it works. You've been struggling with my construct magic because I haven't been able to explain it properly. But now…" I paused, considering how to phrase it, "now I think I've found a way to help you."

Eris raised an eyebrow, suspicion clear in her gaze. "you sure?"

I raised my hand, focusing on the mana within me. I visualized the concepts that Medea's knowledge had granted me—spatial manipulation, magical boundaries, fields that controlled the flow of mana. With a flick of my wrist, a shimmering barrier formed around me, translucent but glowing with arcane symbols.

"This," I said, "is a bounded field."

Eris's eyes widened. "What is that?"

"A form of magic that controls an area. Think of it as a magical territory where the rules are different. It can enhance, protect, or trap."

Her mouth opened in awe. "You made that just now?"

I nodded. "No I have been researching on it for quite some time but I think I just had a moment of inspiration that cleared many problems I have been facing .And with this, I believe i can help you understand magic more deeply."

The following days were spent refining my understanding of bounded fields. Eris was impatient at first, wanting to return to learning how to create swords from mana, but I convinced her to focus on the basics of bounded field magic.

"Before you can summon constructs, you need to understand the space around you," I explained. "Bounded fields allow us to control that space."

She frowned, crossing her arms. "It's nowhere as awesome as making swords."

I chuckled. "No, but without control, flashy magic will fail. With this, you'll have an advantage in any fight. You can set traps, enhance your power, and weaken your opponent—all before drawing your sword."

Eris still seemed skeptical, but I could tell she was intrigued. She started practicing under my guidance, trying to create basic barriers. At first, her attempts were clumsy, but soon, she managed to create a faint shimmer of energy around herself.

"You're getting there," I said, watching as she strained to hold the field.

Eris grinned, sweat beading on her forehead. "This is harder than it looks."

"Magic has never been about strength. This is about understand the world around us and bending it to our will and that definitely ins't an easy feat "

Days turned into weeks, and Eris began to grasp the fundamentals of bounded fields. She wasn't at the level of summoning constructs yet, but her control over mana had improved significantly. More importantly, she was learning patience—something I thought was impossible for someone as impulsive as Eris.

Meanwhile, I delved deeper into Medea's knowledge. Her mastery over bounded fields was terrifyingly advanced. In Fate/stay night, she had created fields that warped space, isolated dimensions, and even blocked powerful attacks from legendary heroes. Right now I am nowhere near being able to replicate everything she did, but the potential was staggering.

I created smaller fields to experiment—shields, barriers, and sensory nets that could detect even the slightest disturbance. One day, while Eris was training, I wove a bounded field around her without her noticing. It was a simple detection field, but it allowed me to monitor her movements and adjust my guidance accordingly.

When she finally noticed, her eyes widened. "Did you…?"

I smirked. "I've been watching your progress. You're getting better."

Eris's eyes lit up with pride. "I didn't even sense it!"

"That's the power of bounded fields," I explained. "You can control everything within the space you create. You'll learn how to do that soon."

As the weeks progressed, I began to see the true potential of the knowledge I had gained from Medea. Bounded fields weren't just defensive—they could be offensive as well. By controlling space, I could limit an opponent's movements, trap them in an isolated dimension, or even warp reality to a limited extend within the field.

One afternoon, I decided to demonstrate the full power of a bounded field to Eris.

"Alright," I said, standing opposite her in the courtyard. "I'm going to trap you in a bounded field created by me. Try to Hit me."

Eris grinned, eager for the challenge. "Easy."

Both of us took the position with 5 metre distance between us. She ran towards me and as soon as I was within her range of attack

I activated the field, and instantly, the space around her shimmered and distorted. She swung her sword, but it passed through empty air, then she realised that the distance between us is somehow still 5 metres

"What the—?!" she shouted, trying again and again to hit me but the result was still the same.

"Within this space," I said, "I control the rules. Your sword can't touch me unless I allow it."

Eris's eyes blazed with determination. "I'll break through it!"

I watched as she attacked with everything she had, but the field held. Her frustration grew, and eventually, she stopped, panting.

"I can't… How do I fight this?"

I released the field and stepped toward her. "That's the power of bounded fields. They let you control the battlefield. But don't worry—I'll teach you how to use them."