|This article is about a/an episode in Kamen Rider Ex-Aid.|
Chasing the Mystery! (mysteryを追跡せよ！ Misuteri wo Tsuiseki seyo!) is the twenty-first episode of Kamen Rider Ex-Aid. It features the debut of Brave Hunter Quest Gamer Level 5 (Full Dragon). It also features Emu's official confrontation with Masamune Dan and a further discovery of Bugster Viruses' origins.
Emu and Hiiro learned from Poppy that Kuroto was the one who had suggested Emu to CR. Meanwhile, a police detective is investigating the Zero Day case, causing him to interrogate Kuroto's father, Masamune. During the investigation, he gets infected by the Game Illness. In order to save him, Emu confronts Masamune.
At a prison, Detective Heiji Uesugi is attempting to speak with the prisoner Masamune Dan, but Masamune walks out; the detective starts suffering from game illness symptoms. Meanwhile in CR, Emu is exhausted from Hiiro's supervision of his surgery internship, Hiiro commenting that fighting Bugsters seems to be all Emu is good for; on that note, Poppy reveals that it was actually Kuroto who had suggested she seek out "Genius Gamer M" to recruit into CR. They get an emergency call and go to the prison, diagnosing Heiji as having the game illness; instead of following them back to CR, however, he insists to see Masamune again (Asuna tells Emu that Masamune is Kuroto's father and the one who caused Zero Day), but his illness breaks out, the Kaiden Bugster taking him over. Emu and Hiiro transform into Ex-Aid Double Action Gamer Level X and Brave Hunter Quest Gamer Level 5 Full Dragon and Stage Select to the woods; Kaiden challenges them to a sword fight, the Riders using the Gashacon Key Slasher and Dragon Blade. Genm Zombie Gamer Level X appears, but instead attacks an arriving Snipe Simulation Gamer Level 50 to retrieve the Gashat Gear Dual β. Brave uses Drago Knight Critical Strike while Ex-Aid uses Mighty Double Critical Strike, but Kaiden deflects several of the hits and is only weakened to the point of retreating back inside the patient. Snipe and Genm target each other with Bang Bang Critical Fire and Arrow Mode Bang Bang Critical Finish, but Snipe's Level 50 attack overwhelms Genm's Level 10 defense and launches the Bang Bang Shooting Gashat back to Snipe; Genm revives and retreats. Kuroto stumbles back to his hideout, saying that reviving one more time should give him enough death data to awaken the true "Level X", plugging in Dangerous Zombie to charge with something.
Back at CR, Heiji insists he's fine and tries leaving, but collapses out of the patient bed. He reveals that the Bugster virus killed his son on Zero Day five years ago and he's been investigating the event ever since; Masamune has admitted some responsibility, but never elaborates on how the Bugster virus came about. He also notes that both Kiriya Kujo, who visited Masamune, and Kuroto Dan, his son, are missing. Emu vows to help investigate to find out why Kiriya was killed, and though Hiiro says that isn't a doctor's job, he leaves with Asuna anyway. Meanwhile, Nico is celebrating Taiga's retrieval of Bang Bang Shooting; Taiga has an idea on how to beat Dangerous Zombie's immortality. Emu and Asuna meet with Masamune to learn what he told Kiriya, but are surprised when he asks them to stop his son. Taiga and Nico go to Genm Corp. to bribe Tsukuru into making them a new Gashat, one of a game where the player kills an immortal zombie.
On their way back to CR, Emu and Asuna are met by Kuroto. Emu reveals what Masamune had said, that the Bugster virus was born from the Y2K fiasco seventeen years prior; additionally, Kuroto had caused Zero Day and blamed his own father. At CR, Hiiro asks Heiji if looking into the past is worth it, remembering Saki; however, thinking about his failure to solve Zero Day makes Heiji's infection flare, and Kaiden emerges again, Hiiro transforming. Kuroto blocks Emu's attempt to leave, the two transforming to fight. Brave Level 5 Full Dragon duels Kaiden as Ex-Aid Double Action Gamer Level XX faces Genm in a quarry, but an arriving Snipe Level 50 is intercepted by Para-DX Fighter Gamer Level 50 eager to fight. As the fights continue, Para-DX switches to Puzzle Gamer Level 50, nabbing an Iron-Body and two Muscular Energy Items for a Perfect Critical Combo, but is intercepted by Bang Bang Critical Fire and both Riders are knocked out of their transformations, Parado noting Snipe's superior experience and warning that Genm plans to surpass Levels entirely. Ex-Aid's Level XX halves hit Genm with a Gun Mode Action Robots Critical Finish, knocking him out of his transformation as Brave defeats Kaiden with a Muscular Energy Item and Drago Knight Critical Strike, curing and freeing Heiji; Kaiden's debris are collected by Kuroto with the Gashacon Bugvisor. The Riders untransform and Heiji hides as Kuroto explains the "ultimate game", Kamen Rider Chronicle: a life or death survival game where civilians are turned into Riders to fight Bugsters. He proclaims that this game will bring excitement to unsatisfied people, and compares his talent at making this to that of the gods. Emu vows to settle this for Heiji's son, Saki, and Kiriya, but Kuroto transforms again, this time with a giant explosion of purple clouds and lightning. Hiiro explains that "X" is the unknown variable, making Genm's power incalculable. Emu transforms to Ex-Aid Level XX again, hitting Genm with an Axe Mode and then a Blade Mode Mighty Brothers Critical Finish, but Genm fires to intercept the second attack and vanishes.
At CR again, Heiji is confirmed clean of the Bugster virus and vows to find Kuroto's hideout to stop him once and for all. Watching, Poppy admires Emu's devotion to past patients lost as well as current ones, Hiiro agreeing before Poppy steals a bite from his cake. As Heiji climbs out of the patient bed, however, he slips and falls again.
- Emu Hojo (宝生 永夢 Hōjō Emu): Hiroki Iijima (飯島 寛騎 Iijima Hiroki)
- Hiiro Kagami (鏡 飛彩 Kagami Hiiro): Toshiki Seto (瀬戸 利樹 Seto Toshiki)
- Taiga Hanaya (花家 大我 Hanaya Taiga): Ukyo Matsumoto (松本 享恭 Matsumoto Ukyō)
- Asuna Karino (仮野 明日那 Karino Asuna): Ruka Matsuda (松田 るか Matsuda Ruka)
- Kuroto Dan (檀 黎斗 Dan Kuroto): Tetsuya Iwanaga (岩永 徹也 Iwanaga Tetsuya)
- Parado (パラド): Shoma Kai (甲斐 翔真 Kai Shōma)
- Nico Saiba (西馬 ニコ Saiba Niko): Reina Kurosaki (黒崎 レイナ Kurosaki Reina)
- Tsukuru Koboshi (小星 作 Koboshi Tsukuru): Shohei Uno (宇野 祥平 Uno Shōhei)
- Masamune Dan (檀 正宗 Dan Masamune): Hiroyuki Takami (貴水 博之 Takami Hiroyuki)
- Rider Gashat (ライダーガシャット Raidā Gashatto, Voice): Hironobu Kageyama (影山 ヒロノブ Kageyama Hironobu)
- Heiji Uesugi (上杉 平次 Uesugi Heiji): Taro Suwa (諏訪 太朗 Suwa Tarō)
- Kuroto Dan (Teen): Mitsumasa Sato (佐藤 光将 Satō Mitsumasa)
- Guard: Kazu Saeba (冴羽 一 Saeba Kazu)
- Kaiden Bugster (カイデンバグスター Kaiden Bagusutā, Voice): Otoya Kawano (かわの をとや Kawano Otoya)
- Kamen Rider Ex-Aid Level X: Satoshi Fujita (藤田 慧 Fujita Satoshi)
- Kamen Rider Ex-Aid Level XX R: Seiji Takaiwa (高岩 成二 Takaiwa Seiji)
- Kamen Rider Ex-Aid Level XX L: Yuji Nakata (中田 裕士 Nakata Yuji)
- Kamen Rider Brave Level 5: Jun Watanabe (渡辺 淳 Watanabe Jun)
- Kamen Rider Snipe Level 50: Eitoku (永徳)
- Kamen Rider Genm Level X: Yuya Nawata (縄田 雄哉 Nawata Yūya)
- Kamen Rider Para-DX: Kazuya Okada (岡田 和也 Okada Kazuya)
- Kaiden Bugster: Takuma Komori (小森 拓真 Komori Takuma)
- Gashat Used:
- Level Used:
- Energy Items Used:
- Iron-Body, Muscular (2x)
- Speeding-Up, Instigate, High-Jump, Invisible, Confusion, Stretch, Recover, Giant, Emission, Liquefaction, Separation, Dark
- After Genm is first defeated and the other Riders untransform, the Energy Items in the Game Area don't despawn.
- As part of Super Hero Time, this episode aired alongside Uchu Sentai Kyuranger episode 4, Space.4: Dreamy Android.
- Viewership: 4.7%
- Closing Screen:
- Text Color: Pink
- Count at episode end
- Gashats in Ex-Aid's possession: Mighty Action X, Gekitotsu Robots, Shakariki Sports, Bakusou Bike, Mighty Brothers XX
- Gashats in Brave's possession: Taddle Quest, Drago Knight Hunter Z
- Gashats in Snipe's possession: Bang Bang Shooting, Gashat Gear Dual β
- Gashats in Genm's possession: Proto Mighty Action X, Proto Taddle Quest, Proto Bang Bang Shooting, Proto Bakusou Bike, Proto Gekitotsu Robots, Proto DoReMiFa Beat, Proto Giri Giri Chambara, Proto Jet Combat, Proto Shakariki Sports, Proto Drago Knight Hunter Z, Dangerous Zombie, Giri Giri Chambara, DoReMiFa Beat, Ju Ju Burger, Jet Combat
- Gashats in Para-DX's possession: Gashat Gear Dual
- Video Game References in this episode:
- Emu is wearing a shirt that has the number "99" on it made up of dots in Ex-Aid's colors of green and purple. Not only does this foreshadow future events, but it could reference the year 1999, the date the WonderSwan was first released.
- Y2K is mentioned in this episode, an event that doomsday fanatics in the year 2000 believed would make all computers non-functional or glitch out at midnight on January 1, 2000, including game consoles or games with time clocks programmed into them.
- Coincidentally, the flashback to 2000 where the Bugsters first emerged is reminiscent of the Digimon movie Our War Game, as the viruses of Diaboromon and the Bugsters both occurred in the year 2000 and the developing growth of both were visually witnessed by someone with an internet-connected laptop.
- Another concidence is that Bandai Namco owns the Digimon franchise.
- This is the first time Ex-Aid wields the Gashacon Key Slasher in Double Action Gamer Level X.
- This is the first time since its debut that Brave doesn't assume Fantasy Gamer Level 50.
- This is the first time Brave uses an Energy Item in Hunter Quest Gamer Level 5 Full Dragon.
- It is also the first time a Rider other than Ex-Aid uses the Iron-Body Energy Item (Para-DX).
- It is also the first time since it started appearing sitting unused in the background that the Shrink Energy Item isn't seen, though every other revealed Energy Item is.
- Ex-Aid is shown to be able to use his Critical Strike when assuming Double Action Gamer Level X by closing and reopening the Gamer Driver's cover. In the toyline, it's impossible to change the Mighty Brothers XX Gashat's announcements from those of Level X to Critical Strike this way while it's in the DX Gamer Driver, as closing and reopening the cover will trigger the Level XX transformation announcement and do the Level XX Critical Strike announcement indefinitely.
- As of this episode, all living Riders still using a compatible Driver have assumed their Full Dragon modes in Level 5 at least once.
- This episode marks the return of the Game Over jingle since episode 17, now played in full form, and the Game Over announcement since episode 12.
- This is the first time in the series the "Gashun!" sound is heard from the Gashat Gear Dual.
- Kamen Rider Ex-Aid Volume 6 features episodes 21-24: Chasing the Mystery!, Engineered History!, To The Max, Dead or Alive! and Go Together, Embracing Your Ambitions!.
- Blu-ray Collection 2 comes with 12 episodes.
- TV Asahi's official episode guide for mysteryを追跡せよ！
- Toei TV's official episode guide for mysteryを追跡せよ！