- "I" refers to "Ice Age" and "Isaka (the true Weather Dopant)"
- #19 is subtitled "His Name is Accel"; #20 is "Kamen Riders' Style".
Our story begins with the (admittedly) abrupt debut of Terui Ryu, new superintendent assigned to Fuuto PD, asking out heroes for help on a recent Dopant case. Turns out this Ryu is The Stoic and The Ace in one package, and Shotaro can't stand him already. We learn later on that he's been sent over specifically for Dopant cases, and naturally we get one right off the bat:
A near-fatal freezing attack, the latest of several in the past week, is being investigated - and a convenient blue chrysanthemum is their first clue. Then the Dopant itself finally arises, and Ryu's agenda is finally made clear - with the clearly non-police-issue and Gaia Memory-compatible Engine Blade weapon, he's out to take down an ice-using Dopant at any cost. Unfortunately, it slips away, and the sighting of known businesswoman Katahira Makiko at the scene gives them their first suspect.
Makiko owns Fuuto's biggest flower shop Cornflower Blue, responsible for the breeding techniques that created the blue chrysanthemum. She's highly successful but somewhat unpopular, and quite alone when our heroes find her. It doesn't help her case when she makes a run for it and the ice Dopant conveniently appears, leading to Ryu busting out an even bigger surprise - the Accel Driver, turning into Kamen Rider Accel. A bigger shock awaits our heroes as Accel chases down and defeats the ice Dopant, leading to Makiko reappearing, and he's quite ready to kill her as well.
After Shotaro calls him out on it, Ryu takes her into custody - but it's implied that he let her slip out of their grasp just so he can track her down and kill her again. He gets there just in time to see her talking to her son Kiyoshi, the wastrel of the family who's been out of touch with her for some time. Regardless, he charges at her in Rider form with Engine Blade ready - but this time Shotaro is ready, having Phillip come along so they can enable Double as FangJoker and battle Accel to a standstill.
Things are made clearer a little later - Ryu's entire family was frozen to death just after his earning his stripes over a year ago, and the only other clue is that the Dopant Memory used had the initial W. Now Ryu's acting out his personal agenda with both the police and GaiaMemory gear from some masked woman calling herself Shroud - but it's Phillip's turn to call him out, as his making a request at Narumi Detective Agency means Shotaro and company are already involved. Their next course of action: dig a little deeper and find the name of the real culprit...
Katahira Kiyoshi, who got his hands on the Dopant Memory just to strike out at those criticising his mother's business tactics, leading to her trying to take the heat for his actions. The final battle begins as Kiyoshi makes a run for it, and this time Double and Accel take turns to bring him down - but instead of taking his life, Ryu takes him in.
And the last twist to this tale reveals itself as Kiyoshi's Dopant Memory is an I for Ice Age and not a W. Who's got the real W (for Weather) Memory? Well, he's been meeting up with Saeko and Wakana, and has the habit of wearing a suit and bowler and playing the piano...
- Foreshadowing: The premise is about a mother whose son Used to Be a Sweet Kid until he somehow turned into a monster - much like Kamen Rider Eternal.
- When we first see Phillip, he's doing research on the Saint Bernard, an animal known for executing snowy mountain rescues. As in, people who have lost their way. Much like Ryu, who will gain a Morality Pet down the road.
- Shadow Archetype: Ryu to Shotaro. Ryu takes the 'hard-boiled' to an extent Shotaro can only hope for... but it's more of a Deconstruction.