This is something I'm thinking of writing a larger story for.  Let me know if I should.

*Author POV*

Across several universes the main villains were on their last line of defense.

Green Hero: Give it up Shigaraki even with AFO you can't win.

After saying that the ground began shake.

Shigaraki: Oh I'll win alright it's just a matter of time.

Green Hero: What did you do?!

Shigaraki: Your about to find out deku.

*Elsewhere*

Red: Give it up Salem we can stop you now.

Salem: Oh you think so?

White: Why wouldn't we think that?

The ground begins to shake.

Yellow: What's going on?!

Black: I don't know but I think Salem is the cause.

Salem: Very observant but your too late.

*same time*

Red armor: Give it up hades there is no where left for to hide.

Hades: Why would I hide this is exactly where I want to be.

Crimson: We should stop him now Issei.

Issei: Right! Let's go Diabolos Dragon. (He mastered it)

Just then the ground starts shaking.

Hades: It has begun.  Know you've failed.

*Finally*

Swordsman: Give Stella back big brother!

Big Bro: What nonsense are you spouting?  The princess of Vermilion was originally suppose to be my fiance not some failures.

Stella: Ikki Run he's too strong even for you!

Ikki: Then my weakest shall over come his strongest.  Itto.....

He didn't get to finish as the ground started to shake.

Big Bro: Finally now I can Reign over multiple worlds as the strongest.

Across all the world's "holes" began opening up and "swallowing" people sending them to the world of heroes.

*Deku POV*

It has been a few months since the event dubbed the collision of worlds happened.  We also lost Shigaraki in the chaos.  I managed to rescue four girls named Ruby, Yang, Blake, And Weiss.  They told me they are from a world called Remnant.  They are call huntresses as they hunt monsters call Grim who thrive off negative emotions.  They were just about to stop the source of all grim when they were thrown here.  Apparently their foe also came here as now there are grim running around attacking people.  Not only that we got what appears grim reapers that one shot anything if they cut it with their scythes.  We even got vigilantes running around with various weapons and powers.

Deku: What the hell is going on.

Before anyone could say anything my childhood friend and rival bust through the door.

Rival: Oi Deku we got information about where Shigaraki might be.

Deku: Let go then.

Ruby: What are we to do?

Deku: stay here I don't know if he can steal aura or semblances but I don't want to risk it.

Yang: So we want to help.

Deku: You dont got a hero licence even if your not from my world at least follow the rules of it.

As me and Kacchan left we didn't hear what the girls said back in the office.

Blake: We are going to help out anyway aren't we.

Yang: Yep.

*Issei POV*

It has been a few months since Hades did something that threw us into this other world.  Rias has been doing non stop research on the world itself as well as where Hades could have scurried off to.

Issei: Any luck Rias?

Rias: Non.  From what I've gathered this world has no devils, no angels, nor fallen angels.  Magic isn't even a thing.  Though the human populist has abilities called quirks that in and of itself is fascinating.

Issei: Then take a break Rias over working yourself will affect your health.

Rias: I'm fine....

Issei covers the book she was reading and gently pushes it to the desk.

Issei: Am I not Issei Gremory your husband?  Then I should know you just as well as you do.  If we get into a major fight both our teams are going to need both their "kings" in top shape if we are to win this.

Rias: How'd I get so lucky with you?

Issei: saved me from a fallen angel twice, made me your ultimate "pawn" and helped me reach the status of King by making me train till I couldn't anymore.

We share a brief kiss before the door opens up.

Lightning: Rias I.....Ara Ara am I walking in on something good?

Rias: *Sigh* Akeno what's going on.

Akeno: Right the familiars have just come back we might have Hades location.

Issei: Rias just give the word.

Rias: Let move everybody this might be our only shot at going home.

Issei/Akeno: Roger!

*Ikki POV*

I was making my way to where I though my brother was holding Stella.  I kept cutting down these black and red monsters as well as grim reaper looking creatures.  If I saved anyone they just screamed Vigilante before running away.

Ikki: 'What the hell is going on!' Don't worry Stella I'm coming.

*Deku POV*

We ended up in Kamino ward which was destroyed in the collision.  Kacchan and the others stayed behind to fight grim and reapers.  I ended up at a clearing that looked very suspicious.  Not long after me red dragon like armor lands not far away.  Sop. After what looks like a high schooler with black hair and a black sword showed up.

Deku: Do you work for All for One?

Dragon: The hell is an All for One?  I'm looking for Hades do you work for him.

Swordsman: I don't know a Hades I'm looking for my older brother who kidnapped my fiance.

Deku: I don't got time for this I'm bringing you to the police you can tell your story to them.

Swordsman: I don't got time for this.  I'll beat you into submission and find Stella.  Itto Shura!

Dragon: Fine by me.  Let's go Diabolos Dragon!

Deku: I'll stop you here.  One for all full cowl 100%

(Take Eri away and give him the air force gloves)

End?

Like I said it's an idea I had so let me know if this is something worth making an actual fan fic of.