|This article is about a/an episode in Kamen Rider Gaim.|
Yggdrasill's Secret (ユグドラシルの秘密 Yugudorashiru no Himitsu) is the twenty-first episode of Kamen Rider Gaim.
The Helheim Forest will soon destroy the Earth if no one acts on it. Kouta informs Mitsuzane about this fact and says they must do something, but Mitsuzane is hesitant as he already knows the truth. Meanwhile, Kaito examines a photograph taken from within the Helheim Forest and believes he sees a human figure, then goes into the forest to investigate.
Still in shock at Takatora's revelations, Kouta relays what he has learned from him to Mitsuzane, who pretends that he did not know about it beforehand. He says that they should follow Yggdrasill's plans and keep it a secret from the public, but Kouta cannot shake the feeling that there is something more going on. After meeting his brother, Mitsuzane is informed that he only revealed to his friend about the forest, and nothing else about Yggdrasill's other plans, like the "Scalar System" or the "Project Ark", but Takatora later confides to Sid that he only told Kouta anything to see how far the boy will go before breaking into despair.
Meanwhile in the Helheim Forest, Kaito searches the ruins for clues about a strange figure in a picture given to him, and while confronting some Inves sent by said creature, Ryoma reveals to Yoko that he has given Kaito the task to keep him away for a while. However, Sid claims that Kouta may eventually become a hindrance to their plans and asks for Ryoma's permission to finish him off. The professor then agrees, claiming that it would be a good occasion to test the limits of the Genesis Core. While having dinner with his sister, Kouta asks her if she would like to know if the world would be about to end or rather spend her last moments without knowing, and she affirms that she would rather know the truth and face it head on. Later at Drupers, Kouta tells his worries to Bando, who claims that he must be careful when someone asks him to keep a secret, because secrets can be a source of power for those who know it, and thus can be used for evil.
Suddenly, Kouta is informed that some human controlled Inves are stealing money and he, Zack, and Mitsuzane depart to stop them. The three Armored Riders confront the criminals and while Kouta runs after them, Armored Riders Ryugen and Knuckle stay behind to defeat their Inves and recover the money. However, Kouta is stopped by Sid, who reveals himself as the man who sold the Lockseeds to the thugs and Kouta decides to confront him. During their fight, Armored Rider Sigurd overpowers Gaim and reveals that the Yggdrasill Corporation is willing to destroy the whole city in order to prevent the Helheim Forest from spreading into Earth if necessary by using the Scalar System, which is the large ring-like structure that orbits its headquarters.
Now certain that Yggdrasill cannot be trusted at all, Kouta transforms into Gaim Jimber Lemon Arms to turn the tables and pin Sigurd down, managing to get the Cherry Energy Lockseed. However, Ryugen appears in the nick of time to summon an Inves and distracts Gaim long enough for Sid to escape. Meanwhile, Kaito examines the picture and wonders about its meaning and where the strange figure is currently hiding.
- Kouta Kazuraba (葛葉 紘汰 Kazuraba Kōta): Gaku Sano (佐野 岳 Sano Gaku)
- Kaito Kumon (駆紋 戒斗 Kumon Kaito): Yutaka Kobayashi (小林 豊 Kobayashi Yutaka)
- Mitsuzane Kureshima (呉島 光実 Kureshima Mitsuzane): Mahiro Takasugi (高杉 真宙 Takasugi Mahiro)
- Mai Takatsukasa (高司 舞 Takatsukasa Mai): Yuumi Shida (志田 友美 Shida Yuumi)
- Chucky (チャッキー Chakkī): KANON
- Zack (ザック Zakku): Gaku Matsuda (松田 岳 Matsuda Gaku)
- Peko (ペコ Peko): Saku Momose (百瀬 朔 Momose Saku)
- Takatora Kureshima (呉島 貴虎 Kureshima Takatora): Yuki Kubota (久保田 悠来 Kubota Yūki)
- Lock Dealer Sid (錠前ディーラー シド Jōmae Dīrā Shido): Kazuki Namioka (波岡 一喜 Namioka Kazuki)
- Ryoma Sengoku (戦極 凌馬 Sengoku Ryōma): Tsunenori Aoki (青木 玄徳 Aoki Tsunenori)
- Yoko Minato (湊 耀子 Minato Yōko): Minami Tsukui (佃井 皆美 Tsukui Minami)
- Akira Kazuraba (葛葉 晶 Kazuraba Akira): Rika Izumi (泉 里香 Izumi Rika)
- Kiyojiro Bando (阪東 清治郎 Bandō Kiyojirō): Tomohisa Yuge (弓削 智久 Yuge Tomohisa)
- Sengoku Driver Equipment Voice (戦極ドライバー各種アイテム音声 Sengoku Doraibā Kanren Aitemu Onsei): Seiji Hiratoko (平床 政治 Hiratoko Seiji)
- Genesis Driver Equipment Voice (ゲネシスドライバー各種アイテム音声 Geneshisu Doraibā Kanren Aitemu Onsei): Shin-ichiro Miki (三木 眞一郎 Miki Shinichirō)
- Narration (ナレーション Narēshon): Hōchū Ōtsuka (大塚 芳忠 Ōtsuka Hōchū)
- Criminals: Kenji Takechi (武智 健二 Takechi Kenji), Shinichi Nihashi (二橋 進一 Nihashi Shinichi)
- Dancer: Ryoko Shimizu (清水 涼子 Shimizu Ryōko), Kei Namiki (並木 桂 Namiki Kei), Saki Kitakubo (北久保 咲紀 Kitakubo Saki), Chisato Maruyama (丸山 千怜 Maruyama Chisato)
- Lock Used:
- Orange, Lemon Energy
- Cherry Energy
- Arms Change:
- As part of Super Hero Time, this episode aired alongside Ressha Sentai ToQger episode 4, Station 4: Be Aware of the Things You Lose.
- Viewership: 5.8%
- Closing Screen Lockseed Collection:
- The title of this episode is similar from the title of episode 14 The Secret of Helheim's Fruits.
- This episode marks the first time Ryugen and Knuckle use their Rider Kicks in the series.
- This also marks the only time:
- Gaim uses the Burai Kick in Jimber Lemon Arms.
- Knuckle's Rider Kick is shown.
- This also marks the only time: