It starts where we left off, where Y/n is already in his final form, Kamen Rider Dark Zi-O Trinity.

Narutaki takes the first move by firing his attack on Y/n.

However, Y/n was calmed and summoned both his Zikan Girarde and Saikyo Girarde. He then combined his two weapons to form his most ultimate weapon, the Yami Saikyo Zikan Girarde.

Y/n used his greatsword to slash through the firing attack with ease.

Narutaki (monster): You...

Zi-O Trinity: Power... I feel the power flowing within me.

Narutaki then decides to charge towards Y/n.

As Y/n stood still he clashed with Narutaki.

Narutaki tried to damage Y/n, but Y/n didn't take any damage and kept attacking him with huge sword slashes.

Narutaki (monster): Impossible... to think a dark rider would have this much power.

Zi-O Trinity: Of course I have, after all, my aim is to become a king.

Y/n then turned the knob on his Trinity Ridewatch one time, and turned his driver around.

Ziku Driver: Zi-O!

Y/n readies his sword, which starts to glow all dark gold.

Finish Time! Zi-O! Solo Time Strike!

Y/n creates two slashes in a shape of a cross. Then, Y/n sends the cross slash flying towards Narutaki in a circular motion.

Narutaki received the circular cross slash and is seen damaged having the cross scar on his chest.

Y/n then turned the knob on his Trinity Ridewatch two times and turns his driver around,

Ziku Driver: Zi-O! Zi-O II!

Finish Time! Zi-O! Zi-O II! Duo Time Rush!

Y/n splits himself into two, the same ability when he was in Zi-O II form. Then, the two copies attack Narutaki at all sides with extreme speeed, delivering flurries of punches.

While seeing Y/n fighting on the sidelines, Tsukasa then gets up.

Natumi: Tsukasa?

Tsukasa: I'm going to help him. He's doing this for my sake, it's natural I return the favor.

Tsukasa then got out his personal Rider Card.

Tsukasa: Henshin.

Decade Driver: Kamen Ride: Decade!

Tsukasa got out his K-Touch and inserted the Decade Complete card in it.

Then he touched the icons in order...

K-Touch: Kuuga! Agito! Ryuki! Faiz! Blade! Hibiki! Kabuto! Den-O! Kiva!

Final Kamen Ride: Decade!

Tsukasa's own Rider Card appeared on his forehead, and the rest of the 9 Heisei Rider Cards appeared on his chest on his new armor like a photo album.

Tsukasa then puts his Decade Driver on his right side and replaced it with his K-Touch.

Tsukasa then joins the fight with Y/n in attaking Narutaki alongside him.

Zi-O Trinity: Decade!

Decade Complete: Zi-O. Let's finish this once and for all.

Zi-O Trinity: I understand.

Narutaki (monster): Damm you, Decade... I refuse to go down like this. After all, I swore to stop you by my hands.

Decade Complete: That's not for you to decide. How my journey ends along with my comrades who have been with me, will be for myself to decide!

Zi-O Trinity: Because as long as there is evil threatening worlds, the journey as being a Kamen Rider will never end!

Tsukasa then grabs his K-Touch and presses the Decade icon.

And Y/n turns the knob on his Trinity Ridewatch three times, which is his final attack. Then turns his driver around.

K-Touch: Decade! Kamen Ride: Complete!

Ziku Driver: Zi-O! Zi-O II! Zi-O Trinity!

Decade - Final Attack Ride: D-D-Decade!

Finish Time ! Zi-O! Zi-O II! Zi-O Trinity! ...Trinity Time Break!

Y/n's attacks Narutaki with his rider kick, along with his other forms, Zi-O and Zi-O II, and all three are physically attacking Narutaki all at once.

As for Tsukasa, he jumps in the air and all the 9 Heisei Riders in their Final Forms appear together. All 9 then fuse together with Tsukasa and a line of huge cards laid out in front of him, and executes his final rider kick.

After both Y/n and Tsukasa's attack landed on Narutaki together, he was defeated in an explosion.

Y/n and Tsukasa watched for a moment as they achieved their victory and they both de-henshined

Natumi: Tsukasa!

Yuusuke: Tsukasa!

Natsumi, Yuusuke, and Daiki went to Y/n and Tsukasa's side.

Natsumi: Are you okay?

Tsukasa: Yeah.

Daiki: Heh, you always get the chance to steal the spotlight.

Yuusuke: So, it's over.

Y/n: ...Not yet. Am I right, Tsukasa?

Tsukasa: That's right! We still need to find a way to restore the rider worlds.

Yuusuke: But how? Even with Apollo Geist gone, the worlds haven't changed back.

Y/n: I may have an idea.

Tsukasa: Y/n?

Y/n: That Wataru guy and the other riders believed your journey was a waste. I'm not an expert in these things, but I know that every journey is worth it. But it depends on what you've experienced... and what you got from it.

Tsukasa was confused at first, but after a minute of thinking, he's surprised when he found the answer to save all.

Tsukasa: The Rider Cards...

Tsukasa then grabbed his deck of his Rider Cards and looked at it for a moment.

Suddenly, the cards started glowing and floated up to the sky.

A moment is being seen when the cards are circling and the worlds are slowly being splitted away, successfully being restored.

Later, Y/n, Tsukasa and everyone else are in a place somewhere close to the city and looking at the sea right in front of them.

Meaning the Rider World has ceased to exist.

The A.R. Heisei Riders have also been brought back to life, and Tsukasa and the others came to their aid, glad to see them alive.

But then, Narutaki, who is revealed to be alive, appeared to Tsukasa and everyone else back in his human form.

Narutaki: Decade. I'll be the first to admit you've done a good thing. However, my determination to rid of you has not faded.

Tsukasa: Narutaki... When will you learn to quit?

Narutaki: Never. Because so long as you exist, my journey will still continue on. No matter what happens, the day will come when you will destroy the worlds.

Tsukasa: No, I will continue traveling world to world, and continue to save them rather than destroy them. And it's all thanks to a someone who has helped me hardened that resolve.

Tsukasa then turns to Y/n and smiles, which he returns with a smile as well.

Narutaki: Curse you, Decade... This isn't over.

Narutaki then summons a dimensional wall and disappeared.

Y/n: He's gone...

Tsukasa: Yes, but I will be ready. ...I suppose I owe you a thank you.

Y/n: But that would just ruin your mood, right?

Tsukasa: Heh, I guess. Still, I owe you.

Y/n: Oh you're welcome. But I was just passing through, that's all.

Tsukasa: *nods and chuckles a bit* ...Hey, what's that?

As Tsukasa points to Y/n's pocket, Y/n sees it glowing.

Y/n took out the thing that was glowing and discovers it's his last blank ridewatch. Which transformed to the Decade Ridewatch, but it's actually all white.

Tsukasa: What is it?

Y/n: This is what I came to this world for.

Tsukasa: Is that so?

Y/n: *puts his ridewatch away*Well, this is the last time I'll say this. But since we both got what we want, it's time for me to go.

Tsukasa: Did something happen that's causing you to hurry?

Y/n: The world where I come from is going to be destroyed, but now I can finally go back in order to save it. However, there's still something left for me to do, someone important I need to save.

Tsukasa: I see. Well, if you managed to save this world, I guarantee you won't have any problem saving yours. So whatever happens next, I wish you the best of luck.

Y/n: Tsukasa... Right.

Y/n then walks away, but only took a few steps before he froze and turned to Tsukasa.

Y/n: ...Shouldn't you be going too? You are in the middle of a journey after all.

Tsukasa: Yeah, that's right.

Y/n: You know, I've been thinking about what that Narutaki guy said to you before.

Flashbacks then played of how Narutaki is saying all that negative stuff to Tsukasa.

Y/n: And I've been thinking that when a new power rises, it will always be used for evil. But that kind of power, doesn't have to serve only that purpose forever. Because whether power should be used for good, evil, or be destroyed, that's up to the ones who have it in the first place.

Everyone was then silent and Y/n looked up at the sky, while still talking to Tsukasa.

Y/n: But I have to admit, I never imagined that you saved all the worlds in the end. ...The power you have as a rider, is a good power. A true good power... If more people strive to use their power to make a better place for others than themselves, then maybe that's how everyone will live in peace in time.

The riders present were surprised by Y/n's speech.

Y/n: ...Have you found your peace?

Tsukasa then looks down for a second, but looks up to see Y/n already gone.

Tsukasa: Y/n...

Wataru A.R.: Zi-O... Just who are you?

Later...

Y/n is seen roaming around the city.

He's finally succeeded in collecting all of his selection of riders' powers.

But unfortunately, there's still something for him that he needs to do.

Y/n: ...Koemi, wait for me.

To be continued...