Sēx System: Destroying DxD

Infinite Multiverse & Mirror Worlds

The Multiverse is endless, composed of countless Mirror Worlds. Despite variations, every world retains its core essence. 

For example in One Punch Man—key figures like Tatsumaki and Saitama always exist in some form no matter what kind of Mirror World. 

Also, Mirror Worlds can be destroyed of no consequence but if the core world is destroyed all the remaining Mirror Worlds also die, effectively eliminating the world of OPM forever.

The Parasitic Bridge

Tatsuya's System doesn't directly summon beings, skills or items. It creates a parasitic bridge—using what were once called System Points, now World Essence—to extract and copy a target's soul from its Mirror World, reconstructing it under his control.

For context, Tatsuya could spin a wheel that granted him abilities from different fictional characters at random through System Point/World Essence. In one of the spins he had gotten a Summoning Card which he used to summon Tatsumaki. 

Unfortunately, he underestimated her and Tatsumaki chose to self-destruct instead of resigning to her fate of being a slave, filling him with endless rage. He used a forbidden ability to forcefully summon Tatsumaki's copied soul back from the dead and he vowed to torture her to death and slaughter everyone related to her for it.

He also used the System to send the memories of this event to the real Tatsumaki so that she remains in fear till he goes to the One Punch Man World. (Chapter 87 and 88 also till Chapter 92 of Book 1 if curious.)

Feeding on World Essence

Beyond summoning, the System feeds on World Essence—the life force of worlds—to grow stronger. It harnesses this essence by parasitically linking to each world, slowly devouring its strength.

Disrupting Fate

Every world follows a predestined plot enforced by its Heavenly Spirit, which ensures key Fate Bearers fulfill their roles. When the plot is disrupted, the Heavenly Spirit weakens, allowing the System to absorb its essence.

Tatsuya: The Anomaly

Tatsuya (formerly Adrian Frost) is an Anomaly—tasked with breaking the world's destined fate. By interfering with its narrative, he weakens the Heavenly Spirit, paving the way for the System to consume it. 

The System had disguised itself as a Sex System initially to motivate Tatsuya but later revealed that World Essence can be earned in various other ways then simply having sex with the relevant female characters.

A Mutually Beneficial Gamble

The System gambled by choosing a host driven by ambition. Tatsuya leverages the System to ascend, even as he learns that his accumulated "System Points" are, in fact, World Essence. To upgrade from Two-Star to Three-Star, he needs 100,000 World Essence—a sum his usual methods can't cover.

System Update & New Target

At that moment, the System buzzes:

[Ding!]

[Fifth Target—Ichinose Honami]

[Acquired World Essence—5300]

[Main Mission—Become Intimate With Five Main Female Leads! Complete!]

[World Travel has been unlocked. Travel to the next World?]

Tatsuya refuses, but another prompt appears:

[̶D̶e̶v̶o̶u̶r̶ t̶h̶e̶ H̶e̶a̶v̶e̶n̶l̶y̶ S̶p̶i̶r̶i̶t̶?̶]̶

A chill runs down his spine as he senses an anxious gaze from above.

The Threatening Night

Looking out at the exceptionally bright night sky, Tatsuya realizes the Heavenly Spirit has sensed its impending doom. The System's parasitic links, like demonic vines, wrap around the Heavenly Spirit, draining it until it is nearly strangled.

Stepping into the Heavenly Realm

Entering the so-called Heavenly Realm, Tatsuya's first thought is that it appears serene. Yet, the endless white domain's fractured, mirror-like sky arouses suspicion. "Is this really it?" he wonders, his frown deepening.

Pseudo-Spirits & Hidden Presence

The System explains that only fully developed Heavenly Spirits can join the realm; those not yet at Fourth Tier are mere Pseudo-Spirits. Such beings haven't formed their own Heavenly Domain and would be instantly detected—and killed—in a higher-tier world. Tatsuya notes with irony that even Heavenly Spirits have a "childhood."

Commanding the Unknown

Demanding the hidden Heavenly Spirit to appear, Tatsuya's command unleashes golden threads—reminiscent of Soul Eater's strands—that lash out like claws, distorting space and triggering an earthquake. A small tear in the fabric of space appears like jet-black ink on a blank page.

Revealing the Void

At the System's prompt—"Tear it open, Host"—Tatsuya rips the tear apart. Inside, he finds a void of pure, shifting blackness housing a formless, humanoid entity. This being, a chaotic blend of black and white like Yin and Yang, is bound by golden threads and radiates oppressive pressure.

Cosmic Irony & the Final Query

The System notes, "[It might not have developed yet, but its roots belong to Heaven.]" Tatsuya chuckles at the cosmic irony of being trapped in a game of cosmic beings. Then the System abruptly asks, "[Can I devour it?]" At that moment, the Heavenly Spirit trembles, its grief palpable—knowing its end is near but Tatsuya denies.

Heavenly Spirit's Disquiet

The Heavenly Spirit sensed the parasitic threads loosening and grew confused, unsure what more the System could extract from it.

Divine Predation

Unfamiliar with mercy, it remained a natural predator, resenting any lowly beings that dared challenge divine authority—even as anomalies emerged.

The Sole Anomaly

Before the Spirit stood the lone surviving Anomaly, which paid no heed to Tatsuya's human form but fixated on a vast, shattered shadow behind him—a defiant remnant like a fragmented sky.

Impending Demise

Realizing its end was near, the Heavenly Spirit felt only sadness—not mercy—as it clung to its inherent nature of ruthless divinity.

Tatsuya's Taunt

When questioned by the System—"Are you sure, Host?"—Tatsuya smiled and replied, "Yes," challenging the System to act, insinuating the Tier-1 Heavenly Spirit was too insignificant to offer anything more than mere refreshment to it.

The Emergence of a New Form

Suddenly, smoke billowed from Tatsuya, and a distinctly human, ethereal woman emerged—a being with silver hair, a pale, flawless face, one glowing eye, and the other obscured by jagged black feathers.

Ethereal Seduction

Clad in dark, form-fitting attire with a pulsing sigil and surrounded by chaotic black feathers, she glided toward him, her voice a soft, mesmerizing melody, asking if he was displeased with her form.

The Naming and Union

Tatsuya, admiring her beauty despite his frosty demeanor, suggested the name "Kaguya"—alluding to a goddess. In response, she explained her form was crafted during his last System upgrade, designed to seduce him and test his will.

Soul-Bound Destiny

Kaguya declared their souls were now one: if one died, so would the other. This irreversible union meant that Tatsuya and the System were no longer separate entities but a single anomaly, bound by fate and mutual survival.

Inevitable Fate

Even as Tatsuya joked about the absurdity of "selfcest," he recognized there was no escape. The parasite had found its host, sealing their fates as one being—where death for one signified the end for both.

Amasawa's Introduction

Kaguya asks if the being Tatsuya is bringing along is Amasawa. He notes that Amasawa "can't see" her—a comment underscoring her passive role—while hinting that her presence is meant for background observation or a hidden role. 

One of the reasons he has brought Amasawa along is because of her personality, more information in her Character Profile in the Auxiliary.

Humor & Survival Banter

Tatsuya jokes that Amasawa will bring entertainment in the next world, especially if it turns dangerous, adding that a sexless world is no fun. Kaguya teases him that, given his nature, he wouldn't venture out until he's strong enough to survive.

Taking Over the Heavenly Spirit

Kaguya reveals that since Tatsuya refuses to kill the current Heavenly Spirit, she will take over. Her form dissolves into smoke and merges with the Heavenly Spirit, forcing it to tremble and transform into her phantom form.

Limited World Maintenance

Now in control, Kaguya explains she can only maintain this world for a few hundred years because she isn't a true Heavenly Spirit. Tatsuya questions why only real Heavenly Spirits can sustain worlds; her answer is vague, citing rules and blurry memories.

Time-Stopping Demonstration

Kaguya shows her power by flipping her palm to reveal a flowing river's visage. With a pinching gesture, she forms a water sphere that effectively stops time in the world—though she warns it will eventually burst, allowing time to flow again and the world to collapse.

Bridges to New Worlds

She then displays multi-colored threads (originally black but now red, yellow, green, and white) on her palm, each representing different types of worlds:

  • Red: Extremely dangerous (off-limits).

  • Yellow: Dangerous but survivable (recommended).

  • Green: Worlds Tatsuya could dominate.

  • White: Benign worlds like Classroom of the Elite.

Tatsuya chooses a yellow thread listening to Kaguya's recommendation as she says that a Green World will provide limited growth since Green Worlds usually have Heavenly Spirits of the Second Tier. With Tatsuya's strengths devouring a Tier-3 Heavenly Spirit will be much more beneficial.

The thread swirls into a majestic gate, though its specific identity remains hidden.

Departure Through the New World:

Tatsuya, Amasawa, and Kaguya prepare to leave for the new world. Tatsuya leads them through the yellow gate while Kaguya's former, emotionless form watches silently and muses that hope is nothing more than a delusion. The world stands frozen, marked only by the swirling water sphere—an omen of time's eventual return and the world's collapse.