|This article is about a/an episode in Kamen Rider Blade.|
The Challenge to the Past (過去への挑戦 Kako e no Chōsen) is the fifth episode of Kamen Rider Blade.
- Sakuya and Shiori find that Karasuma was using a decoy of his body in order to escape the room.
- Amane goes with Kotarou & Kazuma to the Cave of Echoes and gets poisoned by an Undead.
- Hajime finds out about the Undead and goes to find an Antibody.
- Kazuma helps him by stopping Sakuya from destroying the Undead before they can get the Antibody.
Hajime tells Kazuma that he is no match for him in fighting skill and finds it strange that humans still exist. Kotarou arrives and tell him about Karasuma. Hajime takes the opportunity to escape.
Shiori is still at the building watching the platform where Karasuma was that now holds nothing. She continues to wonder about her father and the unsealing of the Undead. Sakuya arrives and asks her what happened. She tells him and he explains that a trick has occurred. Karasuma used a decoy of himself so that he could disappear unnoticed. Sakuya wonders whether it was to avoid responsibility of unsealing the Undead. Shiori tries to tell him that it was her father but he interrupts and promises to himself that he will find Karasuma. He walks off just as Kazuma & Kotarou return. Kazuma asks him what he did to Karasuma but Sakuya pushes him off and walks off. Kazuma ask Shiori why she didn't tell them when she first found Karasuma. she tells him that she needed to research something first.
At the Jacaranda. Amane asks her mother if she knows of the cave of Echoes which apparently allows people to hear the voices of dead people. Amane tells her that she wants to go there and see if she can hear her father's voice. She asks her but her mother tells her it is just superstition. Hajime follows her to keep an eye on her.
Amane tells Kotarou about the Cave of Echoes and tries to get him to take her but he says no because Haruka would be angry. Kotarou tries to tell Amane that it is just superstition too and that it is fake. Amane insists that she believes and she also promises Kotarou to stop bothering her mother about it if they go. Kazuma volunteers to go as well hoping to his his mother and father's voice.
As they are about to leave, Hajime shows up to take Amane home. Kotarou explains to Hajime that they have already called Haruka and told her about going.They asks Hajime if he would like to go but he refuses. On the way home, he senses something. He hears a monster refer to him as Chalice. Nearby, a Man rolls down his car window and stares at Hajime.
Amane asks Kazuma what he would talk to his parents about. He tells them about the fire and that it was the day that he would save everyone.
Sakuya's friend comes into her office to find Sakuya resting there. He wakes up and apologizes for coming in without permission but she is fine with it and tells him he can come there any time he likes. She changes the conversation and tells Sakuya about Patients who have mysteriously come down with a fever once they have visited the Cave of Echoes. They also mention a centipede Monster of some sort.
Kazuma, Kotarou and Amane arrive at the Cave of Echoes to see that it has been fenced in with a no trespassing sign. Amane goes in anyway, believing that she has a Kamen Rider with her which elicits an interesting response from Kazuma who believes she is talking about him. They all go into the cave and Kotarou tries to get them to rethink it. They hear something and Amane thinks it is her father's voice. She screams and faints. Kazuma and Kotarou go around a corner to find Amane on the ground and an Undead standing over her. Kazuma distracts the Undead by transforming while Kotarou gets Amane out. As Kotarou picks her up, he realizes a blue-colored liquid on Amane's Face. Kotarou tries to wake her up and Kazuma diagnoses that she has a fever. At the hospital, they are joined by Haruka and Hajime. Kotarou tells her about the fever. Kotarou and Kazuma blames themselves and mention to Hajime the appearance of the Undead. and that it spat its Venom on Amane's Face. Hajime runs off mentioning and antibody and Kazuma chases after him. Kazuma tries to get information out of Hajime but Hajime exclaims that there is no time and knocks Kazuma over. Kotarou alerts them to the Undead who is fighting Sakuya. Hajime tells Kazuma that if Sakuya destroys the Undead, he cannot get the antibody.
Sakuya goes to seal the Undead but Hajime in Chalice Form interrupts. He tells Sakuya not to interrupt but Sakuya doesn't care and continues to try and fight the monster. Kazuma arrives and holds Sakuya back so Hajime can get the Antibody. Kazuma realizes that Chalice is Hajime and holds back Sakuya who is ruthless is trying to destroy it. Kazuma transforms to fight back.
Hajime continues to unsuccessfully find the antibody in the Undead's Body as Amane's condition worsens in hospital.
- Kazuma Kenzaki (剣崎 一真 Kenzaki Kazuma): Takayuki Tsubaki (椿 隆之 Tsubaki Takayuki)
- Sakuya Tachibana (橘 朔也 Tachibana Sakuya): Kousei (Hironari) Amano (天野 浩成 Amano Kousei (Hironari))
- Hajime Aikawa (相川 始 Aikawa Hajime): Ryōji Morimoto (森本 亮治 Morimoto Ryōji)
- Shiori Hirose (広瀬 栞 Hirose Shiori): Yumi Egawa (江川 有未 Egawa Yumi)
- Kotarō Shirai (白井 虎太郎 Shirai Kotarō): Terunosuke Takezai (竹財 輝之助 Takezai Terunosuke)
- Sayoko Fukasawa (深沢 小夜子 Fukasawa Sayoko): Urara Awata (粟田 麗 Awata Urara)
- Isaka (伊坂): Yasukaze Motomiya (本宮 泰風 Motomiya Yasukaze)
- Haruka Kurihara (栗原 遙香 Kurihara Haruka): Kaori Yamaguchi (山口 香緒里 Yamaguchi Kaori)
- Amane Kurihara (栗原 天音 Kurihara Amane): Hikari Kajiwara (梶原 ひかり Kajiwara Hikari)
- As part of Super Hero Time, this episode aired alongside Tokusou Sentai Dekaranger episode 2, Episode. 02: Robo Impact.
- A catch-up of the first twelve episodes of Kamen Rider Blade was aired as part of the Super Hero Max 2012 special event on TV Asahi. 
Kamen Rider Blade Volume 2 features episodes 5-8: The Challenge to the Past, Chalice's True Identity, The Trapped Two and The Revived People. It was released on DVD on September 21st 2004, with a total run time of 93 minutes.
Blu-ray Box 1 comes with 16 episodes.