In the wake of the Eternal incident, Gaia Memory cases have been elevated in the mass media, and Fuuto City is the real victim here - Shotaro can only look on forlornly as Fuuto Tower needs to be rebuilt...
...wait, you don't remember that part? Maybe a refresher course is in order...
...which is going to have to wait, as this woman togged out in jungle gear (in the city, yes we know) storms into the scene and demands that Narumi Detective Agency take her case. Meet Kyoko Todoroki, whether you want to or not - Museum staff, if the outfit is any indication, and her raw earnest plus the business end of her bullwhip sums up her mission statement. Someone showing this much determination could only be doing so on behalf of someone they care about, and it turns out this is someone all of Fuuto knows, including Shotaro, Phillip and Akiko, just not in the same way as most... Sonozaki Ryubei. The case itself seems innocuous enough - Kyoko's trying to retrieve something Ryubei's been looking for, the 'Evil Tail', although it's because she'd overheard him and not because he'd put her up to it.
And despite Akiko's warnings, Shotaro takes the case. He and Phillip know what's waiting for them in there, but it just so happens that they're done with walking away.
It's just another day at the Sonozaki mansion, as Ryubei summons Mick with a distinctive wave of his silver spoon, holding Mick's meal in his other hand - a glass goblet full of succulent paté. Yum yum. Yes, the Big Bad of the show is in a better mood than usual - with the Gaia Progressor business in the bag, all they need is Phillip and Gaia Impact, Wakana's destiny as the living conduit to Gaia, will be finalised. Think of it as not losing a daughter, but gaining the world in your hands. Turns out the Evil Tail is instrumental in all this somehow... Better finish that paté quickly, Mick.
Finally, some light is shed on that Sonozaki Elaborate Underground Base - it's an actual dig site that Ryubei managed to claim for himself by acquiring the land, building a convenient mansion over it. Kyoko leads Shotaro into the devil's den to find the Evil Tail... while Akiko manages to tag along and cause just enough trouble to make Kyoko take the bullwhip out. Thanks to that Gaia region-lock, Phillip can't get anything concerning Museum out of the Gaia Library, and staring at the massive cavern walls turns up jack squat, leading Akiko to break out her secret weapons.
Dowsing Slippers. As in, a pair of those green slippers of hers, sttached to dowsing rods. No, really. Kyoko is just about fed up, and probably would have done something nasty if Akiko didn't pick that moment to catch the scent, and get moving.
Interestingly, Phillip also experiences a lucky streak of his own, as his current Gaia Library search turns up a whole bunch of books, labelled Dopant, Gaia memory... everything he'd wanted to know about the Museum outfit, but was afraid to ask. No, really. Even the much-feared volumed labelled Sonozaki Raito is within his grasp... which causes him to panic and get kicked from the Gaia library. Actually it was all Wakana just messing with the settings, but that's not important right now...
No, what's important is that Akiko's special slippers worked, taking our heroes into this hidden corner of the cavern that had partially collapsed... where they find a box that actually says 'Evil Tail' on it. Except they can't open it, and there's no time to work on that when they get an unexpected guest - Smilodon Dopant of all people. Regardless of what it's after, it's Rider time now, or at least once Phillip's out of his brief shock.
Akiko gets Kyoko out of there as Kamen Rider Double and Smilodon Dopant go at it, but unfortunately Smilodon proves fast enough to shake him off and get the Evil Tail box - whereupon the Xtreme Memory shows itself, allowing Double to go into CycloneJokerXtreme. Time for a change of tactic, as Phillip takes advantage of the lifted restrictions and runs a search on Smilodon, allowing Double to anticipate it. Unfortunately, the bad guys up the ante in quite an unexpected fashion, as the walls begin to drip Nightmare Fuel and Terror Dopant shows up in person to claim his prize. Less unexpected however, is the determination Shotaro's showing in the face of Terror Dopant's mere voice, masking the fact that his own phobia for Terror Dopant is still there, forcing Phillip to grab the wheel, take that box and get them all out.
At the same time, Jun Kazu's curiosity has been piqued from his meeting with Ryubei (though you couldn't tell from his face), and he's been asking Saeko just how much she knows about this Gaia Impact business. It's obvious though, that he's just baiting her into action with what little he knows, as he claims he doesn't want her to risk herself in this business. It'd be too much for him to take (though you couldn't tell from his face).
Back at Narumi Detective Agency, Terui Ryu joins our heroes as they assess what they have... the box, for ome thing, and whatever's in it, but Kyoko insists on taking it straight to Ryubei, even though she'd just seen him come for it as Terror Dopant. Akiko elects to tell her about the whole Museum business - the Gaia Memories, the Dopants they created, everything. Until they remember Phillip's stake in all this, and he brings up the way the Gaia Library restrictions have been lifted somehow, but got cold feet when faced with the facts about Museum, particularly the one about himself. Shotaro reasons that he shouldn't blame himself for that... just long enough for Kyoko to take the box and flee the scene.
True enough, Kyoko took that box straight to Ryubei... but her curiosity's been piqued as well. Rather than the explanation she'd wanted though, Ryubei calmly explains to her the very definition of Museum - to preserve nature and history lost through time, despite the effort put into their survival, for one day, even humanity in its hubris will share this fate. His solution - the great ritual everyone had been digging at, which will unite humanity with the planet and ensure its continued existence... by aelecting those most compatible with Gaia Memories and thus the planet itself, while sacrificing everyone else.
It's precisely at the moment when Kyoko nearly hands over the Evil Tail that Shotaro and Ryu show up... which proves to be a mistake, as Shotaro starts relapsing again. It's not a real phobia per se, it's the fact that Shotaro has had to face Terror Dopant far too many times for his own health, and the fear he feels is just the symptoms. Ryu is still fine though, and Ryubei knows about that as well, simply referring him as Shroud's hand puppet. Which will have to do, as Smilodon Dopant shows up again, forcing Ryu to go into Accel and take him on.
Phillip finally bites the bullet and goes back into the Gaia library, finding the Sonozaki Raito volume - and learns a bit more than he bargained for. Yes, he was indeed the son of Sonozaki Ryubei, and apparently Mick was his pet originally, but there's something about the Gaia geyser Ryubei found, the reason he acquired the dig site for his own and spent long hours with his family digging through it... until the fateful accident that day, when young Raito... fell into the Gaia geyser?!
Accel's been having some problems with Smilodon, forcing Ryu to go into Accel Trial. At the same time, Shotaro has gone practically catatonic, until Phillip arrives in person to shake him out of it, and they go into Double immediately. This time Phillip has a gameplan - they go into CycloneMetal and wave the Metal Shaft in the exact same fashion that Ryubei does with that spoon, cueing Smilodon into sitting and staying. Finally, our heroes pull off a Memory Break on Smilodon, destroying it forever... but leaving Mick as he always was. Which causes Ryu to go into a Heroic BSoD of his own.
Before Phillip can bring up what he learned from the volume, Terror Dopant shows up in person and spells it out for him - Phillip's connection to the Gaia Library, along with the Evil Tail, are both needed to complete the Gaia Impact. While Terror's mere appearance sends Shotaro right back to his Heroic RRoD, Ryu as Accel Trial prepares to take on Terror Dopant, who decides to bust out a couple of special tricks he's had... not only can he do a Force push, but the blue part of his oversized headdress can comes off and unfold and grows into Terror Dragon, a massive floating creature the size of a house! Accel Trial's Super Speed proves useless as the creature not only catches up but beats him into submission, just as Wakana shows up to take Kyoko and the Evil Tail.
Finally the truth is out - Raito did fall into the Gaia geyser, which may have given him that Gaia library connection, but physically killed him. The Raito we see here is no longer flesh and blood, just data that left the Gaia Geyser with Raito's consciousness. Why bring all this up now? Because there's nothing short of a miracle than can help our heroes - Shotaro's been hit directly with Nightmare Fuel and reduced to a catatonic shell of a man, Ryu had to be picked out from between the Terror Dragon's teeth, and Phillip himself is down for the count, allowing Wakana to cart him off.
There's not much our heroes can do now - Ryu's laid up in bed, with Akiko watching over him while Shotaro can only cower in a corner, leaving nobody to prevent Kyoko from sneaking off again. At the same time, Saeko finds an invitation in the mail... to her own home. From Ryubei. Jun Kazu reasons that it's more of a show of domination at this point, which pretty much forces Saeko to go.
Phillip finally comes to, in a strange bedroom - though he does get a rough idea where he is, as he makes his way out. Surely with all this decorum it's the Sonozaki mansion - yet having this in mind didn't quite prepare him for what he saw next.
The Sonozaki dinner table, with Ryubei and Wakana and Saeko already sitting there, with Shroud of all people just joining them. Ryubei claims it's just a little get-together for his family, to celebrate the upcoming Gaia ritual, but Phillip just can't put aside that fact that his family is finally together again. Even with Ryubei having brought the Evil Tail to the table to show it off, Phillip tries to make his family see reason. Sadly, this only causes more quarreling amongst them, whereupon Ryubei reveals that the Gaia Ritual is a final threshold for all of them, and this is Saeko and Shroud's last chance to change their minds. Naturally, this only makes things worse as Saeko and Wakana jack in and start wailing on each other... not noticing that Kyoko has already infiltrated the premises. Shroud just gets up and leaves, claiming there's nothing for her here - but not before reminding Phillip of something he'd learned for himself a long time ago.
He has a new family now. Shotaro and Akiko. Shotaro in particular, which she makes sure to repeat to Phillip's face. Which Ryubei simply scoffs at, he knows full well what he's turned Shotaro into and how much good he'll do anymore... at least in his opinion.
Meanwhile, the Cat Fight on steroids between Saeko and Wakana turns into a literal Curb-Stomp Battle as Wakana goes Claydoll Xtreme and beats Saeko into the ground. It turns out a Memory Break by another Dopant is possible too, as the Nasca Memory is shattered at last. Saeko is forced into retreat once again...
...though she's still doing better than our heroes. Ryu's still down and Shotaro can't be expected to hold it together, as the mere Stag Phrone ringtone has him screaming. At least Akiko is there to pick it up... and it's Phillip, who's basically saying goodbye to Shotaro now that he knows the true nature of the Gaia ritual. And he reminds Shotaro that "the courage to ride with a devil" from when they first met is more important now than ever. But that's really not helping the situation any, and Akiko is basically incensed at Shotaro and his crippling inability to act. Which is precisely when Kyoko returns to the Narumi Detective Agency, having succesfully taken back the Evil Tail. Unfortunately she doesn't believe that it'll make a difference, as the true nature of the Evil Tail is finally revealed.
It's time at last for the Gaia ritual to begin. Ryubei starts explaining the finer details to Phillip - Wakana is in the mansion, standing in that spot where they always do their rituals, which they've conveniently placed directly over the Gaia valve in the excavation site below. Not only the Earth's memories, but everything learned from all the battles Double has gone through because of Phillip, all of this has to be channeled into Phillip via the special connection to the Gaia library created by the CycloneJokerXtreme form, and from there it should go to Wakana, connecting her properly to the Earth. Phillip makes one last plea for Ryubei to see reason, but all he gets is... pushed into the Gaia geyser a second time.
And finally, it begins.
The Gaia valve opens all the way in response to synthesising Phillip physically, and sure enough it all spews through the cavern roof and into Wakana, who automatically goes Claydoll Xtreme, causing the geyser of data to spew all the way out the Sonozaki mansion roof, which finally gets Saeko's attention. There's just one little snag.
Akiko, with Shotaro in tow for a change, finally make their way into the mansion and the same chamber Ryubei and Wakana are in... just to bring the Evil Tail with them. Crazy, or foolish, given that it's so important to Ryubei? No, for Shotaro decided that there's something far more important to him.
The Evil Tail is just a regular-looking brush, apart from having the names of the whole Sonozaki family engraved on it. Just a simple gesture of their family togetherness, involving a little something they'd used as a good luck charm. Except now, with the Sonozaki family falling apart in ways that your average soap opera writers would never dream of, it means much, much more, particularly to Ryubei. Indeed, Ryubei had lost his way, destroying the very thing he'd wanted to keep by his side in his path to uniting with the planet and the ultimate power that came with it.
It's worth noting at the point that Shotaro can finally stand on his own feet now. Because he'd already beaten Ryubei there - Ryubei had been left all alone, with Phillip and now Wakana about to become one with the planet, but Shotaro believes that his partner, Phillip can still be brought back. Ryubei simply scoffs at his claim, jacking in and going Terror Dopant as a formality, but Shotaro stands defiant as ever. All it takes is Phillip's words from before and activating the Double Driver from his end, and call for Phillip like he always does...
Which somehow disrupts the Gaia geyser, causing Wakana to go haywire as Shotaro forces the transformation to Double and drags Phillip into himself by force. Finally, Phillip forms part of Double just like he always did, and admits that he should have seen all this coming, the whole reason Shroud made sure to mention that Shotaro was the key to putting things back the way they were. Now there's just the business of ending it.
Unfortunately, Double's luck against the Terror Dopant still hasn't changed, and he even busts out the Terror Dragon one more time to beat Double into the ground - but as if answering the call to heroism, Terui Ryu drags himself out of bed and goes into Accel, taking the RevolGarry along for good measure as they pull a Dynamic Entry on the bad guys. Ryu as Accel in bike form, already hooked up to Gunner-A, comes out with weapons blazing as he declares that it's no longer important why he was given these powers, now that they're his to use. And use them he does, as Terror Dragon shrugs off the first few blasts and bites into Gunner-A, allowing Accel to unhitch and return to the RevolGarry to switch to one of Double's usual components - the Turbuler attachment.
As if reacting to Phillip's now divided presence, the Xtreme Memory locates Wakana on its own, blasting a hole through Claydoll Xtreme in order to fulfill its usual function of transporting Phillip within itself, before it finally finds Double and enables CycloneJokerXtreme. At the same time, Ryu is literally airborne as he takes to the skies as AccelTurbuler, only reverting his upper body to Rider mode in order to bust out the Engine Blade and take the battle to the enemy. Finally, Double and Accel pull their finishing moves at the same time - Double taking advantage of Terror Dopant's Squishy Wizard property to tear him a new one with Double Xtreme, while Accel does so literally with the Engine Blade on Maximum Drive and the Turbuler on ramming speed, tearing through the Terror Dragon on his own terms.
Finally it's over, now that the Terror Memory has finally been shattered - and Terror Dragon falling into the Sonozaki mansion somehow causes it to catch fire as well, just to add insult to injury. There's nothing more for our heroes to do except leave, even as Phillip realises that the Sonozaki family is too far gone - but where's Sonozaki Ryubei, you ask? Why, returning to his house and home of course, as it burns and crumbles about him, and he sees a vision of Wakana, and realises the truth - he's put something into motion that was never really stopped, and Wakana is the key. So why not celebrate amongst the damage instead, with a little dance - just like old times?
It's time to wrap the case as much as they can, trying to appease Kyoko with a cover story - that Ryubei did indeed see the light, with the Evil Tail his constant reminder, just before the end. That's as much as they can figure anyhow, as recovery efforts on Sonozaki property are underway - Ryubei is most certainly gone, Saeko and Shroud are MIA, and... they're not sure about Wakana, because they Never Found the Body.
Because Jun Kazu already did.