|This article is about a/an episode in Battle Fever J.|
The Friend Who Became a Demon (悪魔になった友 Akuma ni Natta Tomo) is the thiry-ninth episode of Battle Fever J.
A sickly doctor friend of Makoto becomes an Egos Monster in hopes of gaining eternal life, even at the cost of his humanity.
Makoto goes to his yearly physical at Johoku University, and his physician and friend Dr. Sekine seems to be showing the signs of an ulcer. Salome lures him to a facility called the immortal club, where they reveal he has malignant cancer and 3 months left to live. They then give him the option of joining Egos and having immortality. Egos turns him into a Jekyll/Hyde type of vampire. Fearing for his friend Makoto asks Kenya to brew him some African herbal remedy, when they discover the vampire. The proximity to Sekine’s condo makes Makoto begin to suspect his friend. Unable to control his transformations, Sekine kills his rival and his supervisor, giving him promotion after promotion. Battle Fever moved to protect his love interest, Noriko and they confirm their suspicions.
- Masao Den (伝正夫 Den Masao): Kouki Tanioka (谷岡弘規 Tanioka Kōki)
- Makoto Jin (神 誠 Jin Makoto): Daisuke Ban (伴大介 Ban Daisuke)
- Kyousuke Shida (志田 京介 Shida Kyōsuke): Yuuhei Kurachi (倉知 雄平 Kurachi Yūhei)
- Shirou Akebono (曙四郎 Akebono Shirō): Kenji Ohba (大葉 健二 Ōba Kenji)
- Maria Nagisa (汀マリア Nagisa Maria): Naomi Hagi (萩奈穂美 Hagi Naomi)
- General Tetsuzan Kurama (倉間鉄山 Kurama Tetsuzan): Chiyonosuke Azuma (東千代之介 Azuma Chiyonosuke)
- Keiko Nakahara (中原ケイコ Nakahara Keiko): Noriko Hidaka (日高 のり子 Hidaka Noriko)
- Tomoko Ueno (上野トモコ Ueno Tomoko): Keiko Kanno (菅野啓子 Kanno Keiko)
- Masaru Nakahara (中原マサル Nakahara Masaru): Takumi Sato (佐藤たくみ Satō Takumi)
- Commander Hedder (ヘッダー指揮官 Heddā Shikikan): Masashi Ishibashi (石橋雅史 Ishibashi Masashi)
- Salomé (サロメ Sarome): Maki Ueda (マキ上田)
- Satan Egos (サタンエゴス Satan Egosu, Voice): Shōzō Iizuka (飯塚 昭三 Iizuka Shōzō)
- Hyde Monster (ハイド怪人 Haido Kaijin, Voice): Takeshi Watabe (渡部 猛 Watabe Takeshi)
- Naoto Sekine (関根直人 Sekine Naoto): Shinji Tōdō (藤堂 新二 Tōdō Shinji)
- Prof. Yasuhara: Kazuya Tokimoto (時本和也 Tokimoto Kazuya)
- Prof. Takamatsu: Gen Miyazawa (宮沢元 Miyazawa Gen)
- Noriko (典子): Misako Okamoto (岡本美佐子 Okamoto Misako)
- Couple: Keiko Yokoyama (横山桂子 Yokoyama Keiko), Kiyonobu Kimura (木村清信 Kimura Kiyonobu)
- Battle Japan: Kazuo Niibori
- Battle Cossack: Hirofumi Koga
- Battle France: Haruhiko Hashimoto
- Battle Kenya: Tsutomu Kitagawa
- Miss America: Eiko Onodera
- This is the second time a person intentionally becomes an Egos Monster; the first was the psychic Bengal Tiger who became the Psychokinesis Monster in episode 4. However the former was a volunteer recruited by Egos, while Sekine was seduced by his sickness into becoming the Hyde Monster.
- Doctor Sekine (and the Hyde counterpart) is portrayed by Shinji Todo; he previously portrayed Spider-Man in the tokusatsu that bridged the gap between J.A.K.Q. and BFJ and will next appear in Sentai as General Hedrer in next season's Denziman