How Nana Shimura Single-Handedly Doomed the Entire MHA World: A Complete Breakdown

Nana Shimura is the single biggest butterfly-effect disaster in the entire series. Every single major catastrophe in My Hero Academia — Tomura Shigaraki, the fall of hero society, the Final War, millions dead or displaced — can be traced directly back to one woman’s series of catastrophically bad decisions made out of fear and grief.

Here is the full, merciless chain of how Nana personally created the apocalypse:

1. The Core Mistake: Abandoning Kotaro (The Original Sin)

Her husband is killed by a villain (possibly All For One himself).

Instead of going into hiding with her son, doubling security, or even just moving overseas, Nana decides the safest thing is to completely sever all ties and dump 5–7-year-old Kotaro in an orphanage with zero follow-up.

She even alters the family registry so he can’t be traced back to her and forbids All Might and Gran Torino from ever checking on him.

She leaves only a vague letter: “Mommy has to fight bad guys, so I can’t come home. I love you.”

Result: Kotaro grows up believing his mother chose strangers over him. He internalizes the message “heroes abandon their families.” This becomes the core trauma that defines his entire life.

2. The Ripple Effect: Creating the Perfect Vessel for All For One

Kotaro becomes a successful but deeply broken adult who hates heroes with religious fervor.

He marries, has two children (Hana and Tenko), and enforces the rule: “No talking about heroes in this house.”

He physically and emotionally abuses Tenko for showing any interest in heroism (exactly like Endeavor did to Shoto, but without the “training” excuse).

All For One — who has been searching for Nana’s bloodline for decades — finds Kotaro effortlessly because Nana never changed her surname on public records and Kotaro never hid his hatred of heroes.

AFO befriends the adult Kotaro, stokes his resentment, and manipulates him into having a second child (Tenko) specifically because he wants a blank-slate vessel with Nana’s bloodline.

Nana’s abandonment didn’t protect her family. It gift-wrapped them for All For One.

3. The Final Trigger: Tenko’s Quirk Awakening

Tenko is bullied, isolated, and abused for years because of Kotaro’s hero hatred (which exists only because Nana left).

One day he snaps, Decay manifests, and he accidentally kills his entire family — including Kotaro, whom he murders intentionally in revenge.

A traumatized, homeless 5-year-old wanders the streets for hours while heroes and civilians ignore him.

All For One finds him and raises him as Tomura Shigaraki.

Every step of this tragedy only happened because Nana abandoned Kotaro.

4. The Meta-Layer: Nana Actively Prevented Anyone From Fixing Her Mistake

She made Gran Torino and All Might swear to never look for Kotaro.

This means that for 30+ years, the two people most capable of noticing something was wrong (a hero-hating man named Shimura with a grandson named Tenko) were forbidden from even thinking about it.

If either of them had broken that promise even once, they would have seen the abuse and intervened.

5. The Vestige World Irony: Nana Admits It Was All Her Fault

In the vestige world she literally says:“The scars I inflicted on him got passed down to Shigaraki… If only I had taken down All For One and gone home to my son… I’m sorry, Kotaro. Your mom was weak.”

She watches Kotaro beat child-Tenko and cries, realizing she created the exact cycle of abuse she was afraid of.

She even asks Izuku if he can kill Tomura because she knows some people can’t be saved — acknowledging that her mistake may have made her grandson into a monster beyond redemption.

6. The Scale of the Disaster

Because of Nana’s one decision:

Tomura Shigaraki exists

Decay exists (AFO replaced Tenko’s original Quirk with a modified Overhaul)

The League of Villains forms

All Might is forced into retirement

The Paranormal Liberation War happens

Japan collapses into chaos

The Final War kills untold millions

All For One nearly wins twice

Counter-Arguments (and Why They’re Wrong)

“But All For One would have found them anyway!” → No. AFO only found Kotaro because he was a public, openly hero-hating adult with the surname Shimura. If Nana had kept her son and raised him normally (or even just stayed in contact), AFO would have had no trail.

“But she had to protect him!” → Plenty of heroes have families. Masaki (Geten’s ancestor), Hawks’ parents, the entire Wild Wild Pussycats — none of them abandoned their kids. Nana’s solution was the single worst possible one.

“She didn’t know AFO would groom her grandson!” → She knew AFO was the kind of monster who would target families. That’s why she abandoned Kotaro in the first place. She just never considered that her abandonment would create the perfect psychological profile for AFO to exploit.

Final Verdict

Nana Shimura is the tragic architect of My Hero Academia’s entire apocalypse.

She is simultaneously:

One of the kindest, most heroic characters (mentored All Might, died smiling, believed in saving hearts)

And the single person most responsible for creating the greatest villain in the series

Her good intentions, cowardice, and refusal to trust anyone else with her family directly caused the end of the world.