For most of Mushoku Tensei, Nanahoshi Shizuka pursued a single goal: returning to Earth.
Unlike Rudeus, she had never wanted to build a new life in the Six-Faced World.
She had been summoned in her original body, separated from everyone she knew, and spent years researching summoning and teleportation magic in hopes of finding a way home.
By the end of the series, she succeeded in creating what should have been a functioning inter-world teleportation device.
Yet despite all of her efforts, she still could not return to Earth.
The reason was far more complicated than a failed experiment.
The First Breakthrough
Nanahoshi’s research took a major step forward after Rudeus agreed to supply the enormous amount of mana her experiments required.
Together, they activated an experimental summoning circle that successfully pulled a plastic water bottle from Earth into the Six-Faced World.
This proved that objects could cross between worlds.
For the first time, Nanahoshi had undeniable evidence that inter-world transportation was possible.
However, she understood that transporting a small object was only the first step.
Sending a living person safely across dimensions was an entirely different challenge.
More Than a Decade of Research
After the successful experiment, Nanahoshi dedicated more than ten years to expanding her research.
She studied ancient teleportation circles, analyzed the principles behind teleportation magic, and gradually uncovered knowledge that had long been forgotten.
Instead of merely copying ancient magic circles like most magicians, she sought to understand how they actually functioned.
Every failed experiment provided new data.
She carefully recorded the magical residue left behind after each test, adjusted her designs, and repeated the process countless times.
Because Nanahoshi possessed almost no mana herself, Rudeus remained essential throughout the project, providing the tremendous magical power required for many of the large-scale experiments.
Perugius’ Contribution
Although Nanahoshi led the research, she did not accomplish it alone.
One of the most important contributors was Perugius Dola.
As one of the oldest and most knowledgeable magicians in the world, Perugius recognized the significance of her work and provided resources that no one else could offer.
He allowed Nanahoshi to conduct her research inside his floating fortress, shared his extensive knowledge of ancient teleportation magic, and assigned his spirit servants to assist with both construction and experimentation.
With Perugius’ support, Nanahoshi built an enormous three-dimensional teleportation device consisting of roughly 25,000 engraved stone tablets connected by an intricate magical framework.
The completed apparatus represented the greatest teleportation project ever undertaken in the Six-Faced World.
The Device Worked… Until It Didn’t
After years of research, the day of the final experiment finally arrived.
Rudeus supplied the immense amount of mana required to activate the device.
Perugius and his servants maintained the magic circle.
Everything proceeded exactly as expected.
Then, at the final moment, the teleportation suddenly collapsed.
Part of the magic circle broke apart as though an invisible force had disrupted the spell.
The transfer failed before Nanahoshi could return to Earth.
What made the failure so mysterious was that neither Nanahoshi nor Perugius found any flaw in the device itself.
From every measurable standpoint, the machine should have worked.
Something outside their understanding appeared to have interfered.
The Truth Behind Nanahoshi’s Summoning
After the experiment failed, Nanahoshi reconsidered everything she had learned about her arrival in the Six-Faced World.
She already knew that she had not been reincarnated like Rudeus.
She had been physically summoned from Earth.
The truth behind that summoning was eventually revealed in Prologue Zero.
In the original timeline, a boy from Earth named Shinohara Akihito was summoned into the Six-Faced World.
Unlike most isekai protagonists, Akihito possessed no extraordinary abilities.
He was forced into a war and eventually lost his life.
His death devastated the Playback Miko, who had grown deeply attached to him.
Unable to accept that future, she unleashed the full power of her ability and rewrote history itself.
Rather than attempting to resurrect Akihito, she altered the past to create a new timeline in which he could survive.
That alteration created a distortion in space-time.
Rudeus’ soul passed through that distortion first and reincarnated decades before the Teleportation Incident.
His existence gradually changed the course of history and weakened the world’s resistance to further interference.
Eventually, the Playback Miko’s second attempt succeeded, and Nanahoshi was finally summoned into the Six-Faced World.
The enormous release of mana from that unnatural summoning triggered the Fittoa Teleportation Incident.
Why Nanahoshi Believed She Could Not Return
After connecting these events, Nanahoshi reached an important conclusion.
She believed that her summoning had never been an accident.
Instead, she believed she had been brought into the Six-Faced World for a specific purpose.
That purpose was not simply to build a method of returning home.
It was to prepare for Akihito’s future arrival.
By spending decades researching inter-world teleportation, Nanahoshi created the only known method capable of sending someone back to Earth.
However, Akihito had not yet been summoned.
If Nanahoshi returned before he arrived, there would be no one capable of teaching him how to operate the device she had spent years developing.
She therefore concluded that history itself required her to remain until Akihito fulfilled his role.
Only then would both of them be able to return to Earth together.
Did the World Actually Prevent Her Return?
This is where the story intentionally left a mystery.
The novels never explicitly stated that the world itself prevented Nanahoshi from returning.
They only confirmed that an unknown force interrupted the teleportation despite the device functioning correctly.
Everything beyond that came from Nanahoshi’s own reasoning.
She interpreted the failure as evidence that her purpose in the Six-Faced World had not yet been fulfilled.
Whether that interpretation was completely correct remained unconfirmed by the end of Mushoku Tensei.
Final Thoughts
Nanahoshi’s inability to return to Earth was never the result of incomplete research.
She successfully proved that inter-world transportation was possible, spent more than a decade perfecting the technology, and built the most advanced teleportation device ever created.
Her final obstacle was not a scientific one but a mysterious force tied to the world’s rewritten history.
By the end of the series, Nanahoshi believed that she had been summoned to ensure Akihito’s future survival.
Until that purpose was fulfilled, she believed she could not leave the Six-Faced World.
Whether that belief was truly correct remains one of the biggest unanswered mysteries in Mushoku Tensei and is expected to be explored in the future sequel centered on Akihito.
