Izuku Midoriya, a 16-year-old student of class 1-A at UA, faces the demon king All For One who has bonded with Tomura Shigaraki's body in one last battle to decide the fate of the world. With the weight of the world and the help of his classmates, he pushes through All For One's defenses for one last attack. He uses his remaining energy to land one last punch to Shigaraki's body as he clashes with Shigaraki's palm and all 5 fingers touch his fist, causing his decay quirk to activate and slowly decaying Izuku's body

Shigaraki: Look at that, we ended up destroying each other... How poetic, the hero and the villain are defeated by each other...

Izuku: Shigaraki... I fought to stop you because I could not forgive you, for what you've done. I wanted to stop you because you wanted to be stopped. So your sadness couldn't be passed on.

Shigaraki: Ha... Even when you knew you could die trying?

Izuku: Especially when I knew I could die trying... because I know you wanted to be saved, and I couldn't let go of someone who wants to be saved.

Shigaraki: Ha... Spoken like a true hero, Izuku Midoriya... If we ever meet again, with the same situation, would you save me again?

Izuku: Nods As many times as it takes

Shigaraki: His body slowly disappears Ha... I'm lucky to have met someone like you. Thank you, Izuku Midoriya... For saving me...

Shigaraki's body has decayed into nothingness, and Midoriya's body is about to be in the same state as well, as he falls to the ground

Izuku(Mind): Mom... I'm sorry I have to leave you behind... All Might... Thank you for trusting me with your quirk, and your dreams... Kacchan, I hope you become a great hero in the future... Everyone... Thank you for making my dream come true... Smiles in his last moments and closes his eyes

Bakugo shoots toward Midoriya, trying to catch him, but it proves futile as the decay process is complete, and his remains flow with the wind. Bakugo lands on the ground before shouting out of pure anger. The rest of the world could only watch in silence and sadness as the kid who saved the world died in action, Inko could only cry at the loss of her only child. All Might couldn't help but react the same way at the loss of his son figure. Uraraka heard what happened and wallowed in sadness as well at the loss of her crush who she couldn't confess in time.

Izuku, waking up to a seemingly vast land with a sea of stars above him as he was breath taken by the sight.

Izuku: Wow.. Am I in heaven?

??: Nice try kid, but not exactly

Izuku: Surprised and looks around Who's there!?

A figure walks towards him (the pic is for clothes reference)

??: Easy there kid, I won't harm ya

Izuku: Okay, then who are you?

??: You may refer to me as Neo, the observer of stories

Neo: And you Izuku Midoriya, are a chosen individual for Isekai

Izuku: Isekai? As in like I'm going to a fantasy world?

Neo: You could say that. The world you are going is a unique one

Izuku: How so? Is it the same formula as most fantasy worlds regarding the Isekai genre?

Neo: Not exactly. To put it in simpler terms, this world named "Remnant" is filled with monsters of destruction called "Grimms" Shows him several pictures of different types of Grimms. The Grimms have terrorized humanity until humanity has found a way of combating the Grimms using crystals called "Dust" Shows him a dust crystal. Humanity used these crystals as energy sources and weapons of combat. It also brings forth occupations of huntsman and huntresses, individuals who are trained to combat the Grimms. You could say that they're a version of the hero occupation in your world.

Izuku: I see, this world sounds amazing Tries to take out his notebook and remembers he's dead oh, right

Neo: That is a simple fix Snaps his fingers as a notebook and pen appear and gives them to Izuku I call it "Analyst", a notebook and pen that will note anything the user desires into perfect information

Izuku: Grabs it with beaming eyes Thank you Neo-San! Bows respectfully

Neo: The notebook should contain all the information you need about this new world

Izuku: Convenient

Neo: Oh yeah, before I forget. In this world, there is no concept of quirks, but rather Semblances. They function like quirks being superpowers but in their own right. They are the manifestation of one's aura and vary from person to person

Izuku: I see... Notes down the information So I'm guessing I'll be getting one as well

Neo: Correct, I have a special Semblance for you that will remind you of your hero days Manifests an orb and hands it to Izuku.

Izuku: Grabs the orb as it gets absorbed into his body Woah...

Neo: Your semblance is called "One For All", not to be confused with your quirk One For All, this Semblance can increase your stats exponentially with strong emotions and the bonds that you've made. It can also strengthen those you've befriended with

Izuku: Wow, really makes more sense with the name One For All than my quirk

Neo: Yup, Anyways, here's some essentials and some money for the new world Snaps his fingers as he's given a bag with his new equipment

Izuku: Takes a look at his new equipment Everything should be set

Neo: One more gift for the road Gives him what looks like his Full Gauntlets and his red shoes

Izuku: Grabs them and puts them on They fit perfectly. Do they supply anything new?

Neo: Aside from being able to amplify your legs and arms strength, making yourself a lot stronger, they can also utilize Aura and Dust

Izuku: Amazed and notes it down

Neo: Of course, you will need to regularly train your body like you've always have

Izuku: I see, Thank you for everything Neo-Sama Bows again

Neo: It's no problem Izuku Midoriya. Now go, a new world awaits you Open up a portal to the world of RWBY

Izuku: Nods and goes through the portal as it closes

Neo: Prepares the space to observe the new story unfold Now, show me what you're capable of, Future hero of Remnant

As Izuku stepped into the portal, his body started to tingle and ache as he braced himself for a new chapter of his life in a new life...

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Izuku: Wakes up and looks at his surroundings So, this is Remnant...