High School DxD: Chaotic Destruction

"Why didn't you tell me?" I asked while looking at Asia who had her head lowered. Asia didn't know what to say, and to that I chopped her head, causing her to cry in pain while holding her head. She looked at me with a tearful look, but she was simply answered with my glare.

"I'm your elder brother. It's my responsibility to ensure your life is stress-free. I don't want to see you ever cry again. If you have troubles, come burden me with them," I said calmly, to which she nodded. She should have told me if she were in the supernatural world, as that world was dangerous. 

"Now, to start with your training. You have a high talent for magic, so I will start by teaching you the basics of magic. You're not much of a fighter, so we should look into summoning magic." I said calmly, to which Asia nodded, ready for battle...

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"Your boosted gear boosts your strength by... no, it's not 2 times every 10 seconds," I said while looking at Issei who gave me a confused look. Boosted Gear is a red gauntlet housing Ddraig, the Red Dragon Emperor, which allows the user to double their powers every ten seconds without limit until the user reaches their limit, whether it's their physical abilities, magic, or demonic power based on the user. It has been described as allowing the wielder to surpass the powers of God and the Four Great Satans for a temporary amount of time.

"If your power doubles every 10 seconds, you would be the strongest in like a minute. Let's give your current power level the number 80. Using that sacred gear, your power would increase to 160, in 10 seconds it would be 320, in 20 seconds it would be 640... using that 10 times, you would have a power level of 81,920, you would be over 1,000 times stronger." I said calmly 

"That Sacred gear instead seems to add buffs on top of each other, with every buff being less effective than the last," I said calmly,

"But that's not important right now, what you need to do is start training your physical capability," I said while snapping my finger, having the gravity hitting Issei to double.

Continuous use of Boosted Gear's doubling abilities will continue to drain the user's stamina, burdening their body far more than other Sacred Gears. If the user reaches their limit, the Boosted Gear will enter its Burst state, signifying their limit, where the user will or has exceeded their physical limit.

"Fight me with everything you have. If you had any other sacred gear, it would be useless. But the Boosted gear is perfect for you. Your personality adding the boosted gear would bring out your full potential." I said calmly,

"So, for the next 10 days, fight me with everything you have. If you fail to impress you, I shall curse you with a spell which makes females near you see you as a friend." I said with a smirk, Issei's eyes widened for a moment, not believing I would be so evil.

"wasting time? Are you going to allow me to make the curse worse? Fine, now the curse would shrink your dick by 1cm every day until it completely disappears, and replace it with a female body part. I would want to see how you can put together a harem as a woman... well, a reverse harem would do." I said with an evil grin. Issei lowered his head, today he had learned what true evil was... and it scared him.

"You bastard!" Issei roared, the boosted gear awakening a new form. In this new form, It has the same appearance as the original Boosted Gear, except with a second jewel that grants the user the Transfer ability and that covers more of the user's arm. As of this moment, Issei can take the power the boosted gear gave him, and gift it to others, for this reason, this final form of the boosted gear is called, Boosted Gear GIft.

"Show me the true power of a pervert," I said calmly, creating a spell that would make Issei not touch my sister...

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"The power of destruction... funny that you have such power," I said with a smile seeing the huge orb of destruction that Rias had created.

"Why so?" Rias asked in confusion, 

"You would see during my battle with Riser," I said while throwing a rock toward the sphere of destruction, causing the power of destruction to cave in upon itself. This left Rias' eyes wide as that was a simple rock that was thrown at high speed. Although it was destroyed, it was enough to deal with her power.

"Destruction can never be controlled, and all you can do is channel it to destroy what you wish. Don't have it try and take shape. Destroy wants to destroy, not look cute or cool." I said with a smile, to which Rias paused not knowing it that was a smart idea.

"Don't worry, you can't destroy me," I said with a smirk, making Rias' eyes narrow as a part of her saw that as a challenge. But she stopped herself.

So, she held out her palm, and not trying to control the power of destruction, she had it shoot forward... but it came out like water, going everywhere and destroying everything in its path.

"What happens when you shoot water at a slow speed?" I asked to which Rias' eyes widened lightly, realizing her mistake. So, this time she moved, shooting a huge beam of destruction towards me. Everything in the path of the beam was erased, all but me who caught the beam with one palm and destroyed it.

"Y-you destroyed the power of destruction?" Rias said in shock while breathing heavily, there wasn't much control behind that attack, therefor she had used up far more energy than needed.

"Did you really think just because it was the power of destruction, I wouldn't be able to destroy it?" I asked with a smile.

"Well, looks like we need to work on your energy control to avoid magical energy wastage. We also need to work on controlling that power, you were targeting me, but so much power was wasted destroying the ground." I said while looking at the huge gap between myself and Rias.

Well, everyone was training... and seeing the potential everyone held, I knew one thing for sure... this world was doomed. For this reason, I was working on getting stronger... don't look at the fact I wasn't training, I'm always getting stronger. I have created many spells, such as [Auto Workout], a spell that makes my muscles go through the burden of working out without me having to work out.

"Well... that might be useful," I said while looking at something known as the dimensional gap. Maybe it wasn't so weird that I just appeared in this world, maybe that dimensional gap was the key to saving this world. 

So, I spent the remaining 10 days within the dimensional gap, exploring the place and learning all of its secrets... and there were a lot.