|This article is about a/an episode in Kamen Rider Blade.|
Immortality's Mysteries (永遠の命の謎 Eien no Inochi no Nazo) is the fourth episode of Kamen Rider Blade.
- Kazuma continues to worry about Sakuya's and consequently, his body falling apart
- Shiori goes to a building where she finds Sakuya & Chief Karasuma. Sakuya tells her that Karasuma and his researchers were the ones that released the Undead.
- Shiori begins to question whether her father was one of those researchers.
- Hajime searches for the Undead responsible for the Melting Photos and the Golden Powder in his Room
- After destroying the monster, Hajime & Kazuma turn on each other
At the house, Shiori refuses to believe that Karasuma really was the one that undid the seal but Kazuma tells her what Sakuya said. He asks he if she knew anyone else who worked with Karasuma on the project. She says that she doesn't know and insists that Sakuya is deceiving Kazuma. Kazuma explains however that it was the first time he had ever seen Sakuya like that, being beaten around easily by an Undead. He worries in front of the other two about his body suffering the consequences of the rider system. Shiori gets up and tells him that if he imitates Sakuya, then he won't fight him either. She accuses him of being afraid to fight which enrages Kazuma. He yells at her, and she yells back at him saying that he will search for Chief Karasuma by herself as she believes she is the only one that believes in him before storming out of the room.
Kazuma asks whether anyone cares about his feelings and how he is falling apart. He says that she doesn't understand. Kotarou explains that she probably does but she trusts a lot in Chief Karasuma. Shiori walks down the street frustrated at the fact that Karasuma may be responsible for the unsealing of the Undead. She remembers back to her first day at BOARD. Karasuma tells her that he has always wanted to work with her and that she should continue helping with his research. He takes her for a tour explaining all about Humanity's Foundation. He explains to her that if they were to able to find the basis for eternal life, then all conflict would end. She realizes something and takes out a picture of someone.
Back at the house, Kotarou gets a call from Amane who tells her about the photos that melted. Kazuma and Kotarou both go over to find that the photos have in fact melted and they theorize that it was probably from something very hot. Kotarou asks them if anything else strange has happened and Amane tells them about the raining Gold Powder. Hajime offers to do something and Kazuma asks him if he understands what is going on. Hajime tells him that he doesn't which frustrates Kazuma who in turn tells Hajime not to take thinks so trivially. Hajime tells Kazuma that they are in shock but Kazuma gets even more frustrated. Kotarou tells him to stop fighting and that they will look at it. Hajime walks off. Amane explains that considering it was Hajime's Room, that he feels responsible for what happened and whats to solve it. Haruka stats to worry about the compilation of strange things occurring, such as the Undead attacking Amane and now the Gold Powder and melting photos. Kotarou tells her to stop worrying. Hajime runs out the front of the Jacaranda and tries to sense where the Undead is. Meanwhile, the Undead with it's powder manages to suffocate a woman and her child in the forest. Hajime begins the search on his motorcycle.
Shiori makes her way to a building where her father used to work and is most likely a part of BOARD. Sakuya walks around the corner and sees her from behind. Shiori walks down a path near a building and find's Chief Karasuma's wallet proving that he is in the complex. Sakuya comes clean and tells her that Karasuma is here. She demands that he return Karasuma but Sakuya refuses and tell her to come with him. They enter one of the rooms where Karasuma is lying on the bed. She runs to help him, but Sakuya tells her not to, informing her that the wires connected to him are acting as a life-support. Shiori asks him what he did to the Chief but he says he didn't do it. He tells her that when he was watching the bugs hatch out of their shells at BOARD, he tried to shoot them all but some of the bugs survived and attacked BOARD. Shiori tells Sakuya that she doesn't believe him and that she saw the security footage of him attacking Karasuma. Sakuya explains that Karasuma was originally going to try and fight the Undead himself and that he had to knock him out to escape from the Bugs. He also explains that it would be bad for him if he let Karasuma die. Shiori asks if his body is really falling apart.She asks him who released the Undead Seal, and Sakuya tells her that Karasuma and his researchers did, and that he has been trying to wake her up to find out more information about it. Sakuya then asks her is her father was on BOARD but she says that he would never do something that dangerous. She remembers back to her father at their mother's hospital bed. Sakuya demands that she tell him if she knows anything. She says she doesn't know anything. He tells her that he had a dream and that he naively believed that he was fighting for humanity. He tells her that she is free to visit Karasuma whenever he likes, throwing her the keys. He leaves and she continues to try talking to the chief.
Later, Shiori returns and Kotarou questions her on why she took so long. She asks for Kazuma but as soon as he comes over, she says nothing to him and runs upstairs. She questions whether in an attempt to save her mother's life, her father released the seal on the Undead to try and find the answer to eternal life.
At the Doctor's House, Sakuya's Classmate is nearly finished with a puzzle which depicts her and Sakuya graduating from university. She searches around her desk for the final puzzle piece. Sakuya comes into her room and tells her that he swallowed it. He tells her that he is scared that if she were to finally finish it, that it would end up like himself (i.e Finished). He asks her if he can sleep here again. He sits down in a chair and quickly falls to sleep again. She tells Sakuya while he sleep that she won't finish the puzzle and messes it up.
Hajime continues to search for the Undead at Night.
Meanwhile Kotarou tells Kazuma back at the house that he was worried that an Undead had caused the photos to melt but after investigating, he found no response. Kazuma continues to question whether the Rider system will treat his body the same way as it did with Sakuya's. Kotarou tells him to stop talking stupidly and that he doesn't believe it. Kazuma becomes slightly joyful at the prospect of someone being worried about him.
As Morning Breaks, Hajime is still searching for the Undead and finally is attacked from the side by it as he is riding through the forest. He quickly transforms and starts to fight. At the same time, The Undead Tracker reacts and Kazuma goes to leave before Hirose stops him and tells him that he is not responsible for undoing the seal and shouldn't have to sacrifice himself. Again... Kazuma shows slight joy in having another person worry about him. He runs off to fight anyway. The Undead and Hajime fight fairly evenly with Hajime reflecting shots from the Undead. Kazuma arrives and transforms and goes to help Hajime. Hajime tells Kazuma to continue fighting the Undead while he watches. Kazuma scans his Thunder Card through his sword but gets knocked back by the Undead before he can use it. Hajime by watching the two battle manages to find the Undead's Weak Spot, scans his Tornado Card and shoots an arrow at the Undead's Eye causing it's buckle to unclip. Hajime seals it which becomes the Reflect Card. Kazuma demands to know why Hajime used him as a diversion but Hajime quickly attacks him back. Kazuma tells Hajime that if he thinks of Kazuma as an enemy then he will think of Hajime as an Enemy. Hajime questions whether a human can really beat him and they start to fight.
Shiori brings Kotarou to the Building where Chief Karasuma is and tells Kotarou that they need to get him out before Sakuya comes back. She and Kotarou come in but Karasuma's Body randomly ignites in flames.
Hajime easily takes control of the battle, easily throwing Kazuma about.
Shiori tries to save the Chief but Kotarou holds her back from the flames.
- 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)
- Yoshito Hirose (広瀬 義人 Hirose Yoshito): Junichi Haruta (春田 純一 Haruta Jun'ichi)
- 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)
- Kei Karasuma (烏丸 啓 Karasuma Kei): Kazuhiro Yamaji (山路 和弘 Yamaji Kazuhiro)
- Sayuri Hirose (広瀬 小百合 Hirose Sayuri): Reiko Inoue (井上 れい子 Inoue Reiko)
- Moth Undead(Voice): Katsumi Shiono (塩野 勝美 Shiono Katsumi)
- Cards used:
- Thunder, Change
- Tornado, Change
- Cards obtained:
- As part of Super Hero Time, this episode aired alongside Tokusou Sentai Dekaranger episode 1, Episode. 01: Fireball Newcomer.
- Viewership: 9.1%
- 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 1 features episodes 1-4: The Indigo Warrior, The Mysterious Rider, Their Secret... and Immortality's Mysteries. It was released on DVD on August 6th 2004, with a total run time of 94 minutes.
Blu-ray Box 1 features episodes 16 episodes.