Mirio:....

He lost it...

He lost his quirk....

It all happened so quickly...

Him fighting Overhaul...

Learning that Eri was not Overhaul's daughter but the granddaughter of his boss...

Eri accidentally killing her father...

Overhaul's disgusted with Eri's quirk and her existence...

All of it spiral him into rage...

However...

Shin Nemoto grabs the case of Quirk destroying bullets and Chisaki orders him to fire. Only Shin knows the value of the Quirk destroying bullets and cannot waste a single shot; Shin tries to figure out a way to make Mirio deactivate his Quirk.

Suddenly, Shin realizes that Mirio will do whatever it takes to protect Eri, so he aims his gun at Eri. Mirio immediately jumps towards Eri.

Mirio was able to tell that Eri was endangered because she wouldn't scream or cry whenever murderous intent was directed at her and she would simply close her eyes, be silent and grit her teeth; this was Eri's habit that was engraved in her after living in pain and fear for a long time.

Mirio sacrifices his Quirk to protect Eri.

Mirio has reached Eri while Shin fires the Quirk destroying bullet. Eri opens her eyes and sees a smiling Mirio who is about to be hit by the Quirk destroying bullet.

Eri: (No...Why....?)

Mirio: It's okay...I'm here... heroes protect people...no matter what...

Mirio thinks about his childhood where his family's Quirk made it difficult for them to become Heroes, which is why his father gave up on becoming a Hero.

However, Mirio refused to waver and throughout his life he worked extremely hard to hone his Permeation; eventually, Sir Nighteye saw potential within Mirio and made him his sidekick.

Under Sir Nighteye's guidance, Mirio was able to turn his Permeation into a fully combat Quirk; during this time Mirio along with Tamaki and Nejire began being acknowledged as the Big Three...

Mirio covers Eri as the Quirk destroying bullet is shot into his body which begins destroying Mirio's Permeation...

And just like that...Mirio Togata loses his quirk...

Overhaul: What are going to do now, Lemillion. Face it...you're nothing without your quirk. You can never be a hero again.

Eri: (No...No...It can't be...he lost his quirk...and it's all my fault...)

Mirio:....

Overhau: Due to Quirks, people are entitled to dream and begin thinking that they become people that matter...

To that is why Chisaki believes that these people are sick in the head.

As Shin celebrates his triumph, Chisaki laughs at Mirio's efforts and mocks Mirio for smiling because everything he has worked so hard to cultivate have all been reduced to naught and nothing...

As Chisaki is about to deconstruct the ground, Chronostasis is thrown at him, courtesy of Mirio's kick.

Overhaul: (What?!)

Mirio appears before Chisaki and punches his arm.

Mirio tells Chisaki that all his hard work isn't in vain...

Mirio: Because I am still Lemillion!!!

Mirio is a man who grew to accept his weaknesses and was able to strive to achieve his goals because he acknowledged his weaknesses.

...The same holds true about his heart in that his weaknesses were not something to hide....

Mirio: I won't give up! I won't stop until Eri is safe and sound!

Eri:...!

Chisaki tries attacking Mirio but Mirio is still able to make his body intangible, which causes Chisaki to miss. Shin is shocked that Mirio's spirit hasn't completely been destroyed yet.

Despite being greatly damaged himself, Chisaki mocks Mirio for wanting to be a Hero and to try and save Eri.

Overhaul: That delusional thinking for being the problem with today's society and will cure everyone using Eri's power.

Eri:....

Mirio: Shut up...even if I don't have my quirk no more! I will make sure you won't harm her again!!!! CHISAKI KAI!!!!!!!

Overhaul: *Rage* DON'T CALL ME THAT!!!

Overhaul is about to pierce a spike through Mirio as Lemillion yells out Chisaki's name, much to Chisaki's chagrin.

SMASH!!!!!

Mirio: ?!

Eri: ?!

Suddenly, Izuku and Mikoto 
comes smashing in.

Deku: Eri! Mirio-Senpai!!!

Mikoto: We're here to help!

Eri: (He's here...he came back...)

Mirio: (Midoriya-kun... Yukimura-kun....Thank God...We still might have a chance...)

Overhaul snarled underneath his breath. Things just keep getting better and better...

-A little while earlier-

Mimic: FUCK YOU! LEAGUE OF VILLAINS!!! HOW DARE YOU!!! I'LL KILL YOU! I'LL KILL YOU!

Cut back to the moment when Heroes dealt with and defeated Joi Irinaka, who was still pissed odd that he lost and the League of Villains betrayed them.

The Heroes and Police Force decided on their next course of action. Sir Nighteye and Geysis had located Eri's room and the detective ordered Joi to change the labyrinth.

Detective: Do it.

Mimic:....

However, Joi was unresponsive due to the drug he had taken to boost his Quirk. 

Erasherhead: It's too late..He's now no longer has the power to manipulate the labyrinth. It's a possible chance that  that Himiko Toga and Jin Bubaigawara of the League of Villains was lurking somewhere.

Geysis: Yeah...if only we can information out of them as well...but as usual...like an slippery eel...they managed to escape from within our grasp...

Tsuyoi:....

Sir Nighteye asked Joi about the location of the other members of the League.

Mimic: ...I do not know... I swear...when I found them, I would kill them...

Geysis: Sheesh...This guy got a few screws loose...does he even know the position he's in right now. He can't do anything...

Sir Nighteye: It's plausible that only Shadow Slasher, Gunslinger, Toga, and Twice were in the vicinity.

The Police Force stood on guard preparing for Niko, Juurou, Himiko and Twice in case they returned, while the detective declared that they could not ignore them.

As Aizawa and Geysis tried deciding on the best course of action, Ken Takagi told them to leave the League of Villains to the Police Force and rescue Eri.

Mikoto and Izuku were glad to see that Rock Lock was no longer injured despite the torture that Niko and Toga put him through.

The Police Force agreed on Ken's plan; Ken volunteered to stay and keep Joi in check since he was in no condition to move around. Ken reminded them of everyone else who was buying time for them and told them not to waste it. Sir Nighteye, Izuku, Mikoto, Geysis, and Shota immediately headed out while Izuku and Mikoto had promised Ken to rescue Eri.

Rock Lock puts his faith in both of them.

Tsuyoi: Good luck... Yukimura...
Master...he sure has come a long way...

-Later-

When Izuku, Mikoto, Geysis, Shota, and Sir Nighteye reached a wall, behind which was their objective, Izuku smashes the wall and they come running through.

Izuku sees Chisaki and delivers a One For All: Full Cowl punch to his arm.

Izuku's enhanced punch sends Chisaki flying back.

Geysis: NIGHTEYE! GET TO THE CHILD!

As Sir Nighteye to secure Eri.

Sir Nighteye looks upon his student and is amazed that Mirio Togata has been fighting all by himself against the boss of the Shie Hassaikai and his closest aides by himself and not only managed to defeat the aides as well as injuring Chisaki but on top of all that, managed to rescue Eri.

Sir Nighteye grabs hold of Mirio and Eri. A proud Sir Nighteye praises and congratulates Mirio for everything that he has done.

Mirio: *Weakly* Sir...Nighteye...?

Sir Nighteye: You done a good job Mirio...just...please...rest for now...you done enough...

Mikoto watched the scene beforehand then turned his attention towards Overhaul who gets back up.

Both Mikoto and Deku got into a fighting stance while Geysis and Aizawa went into an defensive one.

The final battle with Overhaul ends here...

Mikoto: (For Eri's sake and everyone else's...It's time we finish things here...once and for all...)