|This article is about a/an episode in Kamen Rider Drive.|
What Can Be Spoken By the Irregular Dead? (不揃いの死者たちはなにを語るのか Fuzoroi no Shisha-tachi wa Nani o Kataru no ka) is the twenty-first episode of Kamen Rider Drive. It is the debut of Mashin Chaser's Triple Tune form. Also, a glimpse of Drive Type Formula is seen near the end of the episode.
Simultaneous murders are going on, and Chase keeps popping up in surveillance tapes. While Kiriko and Shinnosuke believe in Chase's innocence, Go does not. But what is really going on?
Five cases of murders are reported at the same time at different parts of the city, but each victim is killed in a different way. While Kyu leaves for home to search some clues regarding the case, Genpachiro remembers that a security camera captured a picture of the suspect and his bike which surprisingly reveals to be Chase. At the Drive Pit, Go decides to hunt him down on his own while Shinnosuke and Mr. Belt agree that Chase has to be killed. Shinnosuke decides to stick to Kiriko's ideals, but promises to kill him if Chase is truly the cause of the murders.
At a ship, Medic lies about Roidmude 072 and her Reapers' demise at the hands of Drive and decides to take matters seriously. After Chase fully heals, he receives a report that he is followed. After incapacitating Gen and his policeman accomplice, he traps them in a Heavy Acceleration wave. Shinnosuke and Kiriko rush to the scene as Mach appears and fights Mashin Chaser. Shinnosuke as well transforms into Drive, bringing Genpachiro and his accomplice to safety via Dimension Cab and fights Chaser. After Chaser traps Deadheat Mach in a Super Heavy Acceleration, he easily overpowers him until Drive Type Technic stops him and tries to reason with his actions for killing humans. Chaser however reveals that he only defends his own kind and thinks of nothing else, fearing Kiriko and Mr. Belt.
Medic orders Chaser to retreat and let her Reapers fight the Riders. She uses her Roidmude form combined with her ballet performances for her attacks. With her Reapers having joined the brawl, she modifies Roidmude 104's right hand into an arm cannon, which explains the creation of Reaper Legion Roidmudes while Brain watches from afar, now knowing her to be the reason behind Chase's increasing power. She orders her minions to retreat while leaving 104 to handle the rest. 104 uses his newfound weapon in an aerial fight until he is destroyed by Mach's Beat Macher Full Throttle.
At the Unit's office, Genpachiro has revealed the Riders' true appearances and deduces the green and black ones as two other unnamed Riders until he is corrected. Remembering previous cases, Shinnosuke reviews the victims as templates for previous Roidmudes used as human disguises, having spoted one from the picture as Roidmude 037's human form, meaning that the original ones were disposed so that Roidmudes could took their places. Kyu quickly arrived and revealed that Roidmudes can travel through computers using their Cores and 072 from prior went into Kyu's blog. Kyu used his method to track Roidmudes via computer network. Mr. Belt sends the Shift Cars to gather the relation without knowing that all of them have been captured by Medic.
Brain meets Chase in his room and gives him "something" to help Chase in his later confrontation against Drive. While Shinnosuke and Kiriko are patrolling in Tridoron, they pick up Justice Hunter's SOS sign. Mach tails Chase on his bike, but is quickly interrupted by Medic, who has Heart take care for Mach. They arrive at Hunter's spot but the Shift Car attacks Shinnosuke and leads him to Chase, where all 18 known Tire Exchange Shift Cars had been placed under Medic's control. It was revealed that all those murders were nothing but baits as she staged Drive's defeat by stripping him of his subordinates, while Mach is confronted by Heart.
Before the slow-motioned Kiriko and Shinnosuke are about to be killed, Shift Wild and Technic quickly docked themselves into their Shift Car Holders to save their lives. Shinnosuke as Drive Type Wild tries to fight, but is overpowered by the improved Mashin Chaser as well as the enslaved Shift Cars. In the end, Mashin Chaser traps him in a Super Heavy Acceleration, slowing Drive's movements greatly and having the advantage. Mach decides to risk his own safety by delivering Shift Dead Heat to Drive but even as Type Dead Heat, the Super Heavy Acceleration reduces his high combat capabilities.
Drive tries to remind Chaser of his old life as Protodrive which succeeds, but he regains his sense and assumes Triple Tune. Mr. Belt is forced to reveal another secret: he had stored a Type Change Shift Car, but was forced to hide its existence due to the danger it carried. Nonetheless, Drive allows for the Shift Car's arrival, having no longer begrudging Mr. Belt for keeping secrets. The Triple Tune Mashin Chaser deliberates Drive with his attack by using the enslaved Shift Cars to ram into him. However, a strange new Shift Car enters the blaze and gives Drive a new form: Type Formula.
- Shinnosuke Tomari (泊 進ノ介 Tomari Shinnosuke): Ryoma Takeuchi (竹内 涼真 Takeuchi Ryōma)
- Kiriko Shijima (詩島 霧子 Shijima Kiriko): Rio Uchida (内田 理央 Uchida Rio)
- Chase (チェイス Cheisu): Taiko Katono (上遠野 太洸 Katōno Taikō)
- Go Shijima (詩島 剛 Shijima Gō): Yuu Inaba (稲葉 友 Inaba Yū)
- Jun Honganji (本願寺 純 Honganji Jun): Tsurutaro Kataoka (片岡 鶴太郎 Kataoka Tsurutarō)
- Rinna Sawagami (沢神 りんな Sawagami Rinna): Rei Yoshii (吉井 怜 Yoshii Rei)
- Kyu Saijo (西城 究 Saijō Kyū): Kenta Hamano (浜野 謙太 Hamano Kenta)
- Genpachiro Otta (追田 現八郎 Otta Genpachirō): Taira Imata (井俣 太良 Imata Taira)
- Narration (ナレーション Narēshon), Drive Driver's voice (ドライブドライバーの声 Doraibu Doraibā no koe): Chris Peppler (クリス・ペプラー Kurisu Pepurā)
- Heart (ハート Hāto): Tomoya Warabino (蕨野 友也 Warabino Tomoya)
- Brain (ブレン Buren): Shota Matsushima (松島 庄汰 Matsushima Shōta)
- Medic (メディック Medikku): Fumika Baba (馬場ふみか Baba Fumika)
- Eyewitness: Takuma Maruyama (丸山 拓真 Maruyama Takuma)
- Police: Hiroyuki Tanaka (田中 宏幸 Tanaka Hiroyuki)
- Dead Body: Kenta Nitta (新田 健太 Nitta Kenta)
Shift Cars, Signal Bikes, & Viral Cores
- Car Used:
- Type Change: Shift Speed, Shift Technic, Shift Wild, Shift Dead Heat, Shift Formula
- Tire Exchange: Dimension Cab
- Type Used:
- Type Change: Shift Dead Heat
- Tire Exchange: N/A
- Form Used:
- Deadheat Mach
- Mashin Chaser
- Burning Solar, Funky Spike
- Bike Used:
- Form Change: Signal Mach, Shift Dead Heat
- Signal Exchange: Signal Kaksarn (in Zenrin Shooter)
- Form Used:
- Mach, Deadheat Mach
- Form Change: Shift Dead Heat
- Type Used:
- Type Dead Heat
- Core Used:
- Chaser Spider, Chaser Bat, Chaser Cobra
- Tune Form Used:
- Tune Chaser Spider, Triple Tune
- to be added
- As part of Super Hero Time, this episode aired alongside Shuriken Sentai Ninninger episode 3, Shinobi 3: Formidable Enemy Gabi Appears!.
- Viewership: 6.2%
- Closing Screen Shift Car/Signal Bike
- Roidmude Count
- Answer to the episode's question: All of the victims were related as human templates for the past Roidmudes who they used to copy.
- Drive assumes all the forms he's used so far in this episode.
- This is the last time Shinnosuke transforms directly into Drive Type Wild.
- It is also the only time Drive changes into Type Dead Heat from a different form other than Type Speed (Type Wild).
- This is the only time Mach changes into his default form from a different form (Deadheat Mach).
- This is the first time both Drive and Mach have used the Shift Dead Heat Car in the same episode.
- Starting with this episode, the opening song for Kamen Rider Drive would feature scenes from the upcoming movie Super Hero Taisen GP: Kamen Rider 3.
- Yuu Inaba's (Go Shijima) 22nd birthday, falling on January 12th 2015, was celebrated during filming of this episode. 
- Final appearance of Drive's Type Speed Cab.
Kamen Rider Drive Volume 6 features episode 21-24: What Can Be Spoken By the Irregular Dead?, How Can I Use the F1 Body to Fight?, Who Can Stop the Hoax Smile? and What Can Keep Mach Running? 
Collection 2 comes with 12 episodes.