|This article is about a/an ranger in Choudenshi Bioman.|
|Sentai Show:||Choudenshi Bioman|
|First Appearance:||Ep. 1: The Enigmatic Giant Robo Arrives|
|Last Full Appearance:||Ep. 10: Goodbye Yellow|
|Last Cameo Appearance:||Ep 13: Delusional Collection Guide|
|Number of Episode Appearances:||10 (Bioman)|
Full list of appearances
|Actor:|| Yuki Yajima (1-9)|
Mayumi Tanaka (VA, 7-10)
Akiko Nakagawa (Akibaranger)
- ―Yellow4's roll call[src]
Mika Koizumi (小泉 ミカ Koizumi Mika?) was the original Yellow4 (初代イエローフォー Iero Fo?) of the Biomen. She was a photographer who dreamed of following in her brother's footsteps to photograph the wildlife in Africa.
Initially, she is hesitant to join the Bioman team. However, she is convinced when she realizes that if she does not fight, then even the animals in Africa that she loves will eventually be in danger. For someone who is hesitant to do battle, Mika is a powerful and skilled martial artist. In episode 10, she becomes a martyr to save the others, and dies from several repetitive blasts of Anti-Bio Particles from the Bio Killer Gun. The team later gave her a proper funeral while still in her Yellow4 form. In the last episode, Peebo apparently forgot to recall her for some reason in the script though Peebo remembers her during the first appearance of Silver.
- Age: 18 years old
- Weapons: Thunder Sword
- Attacks: Super Electron Holography, Action Flash
- Actress: Yuki Yajima
- Philippine-English VA: Geraldine Oca
The footage for Bioman seen in the first episode of Turboranger ends up using clips that ultimately show both Yellow Four: the original Mika Koizumi and her replacement Jun Yabuki. This is the only compilation with multiple Sentai that show both Yellow Four from Bioman.
- Mika Koizumi/Jun Yabuki/Yellow Four: to be added
Super Sentai Legend Wars
Yellow4 is among The vast pantheon of Rangers who feature in The mobile game
Super Sentai Legend Wars.
Mika is a bit of a loner at times and can be a bit stubborn, although she has a good heart it is shown despite her attitude at times Mika is loyal to the rest of the team even if at times she doesn't show it. She also has the habit of taking pictures at the weirdest times (such as when Biorobo grabbed her in the first episode) and also appears to be a bit of a UFO enthusiast.
At the end of Hikonin Sentai Akibaranger: Season Two, Yellow Four I appears with two other deceased Super Sentai warriors, Time Fire and Abare Killer, before the deceased Akagi, Yumeria, and Luna at Himitsukichi. After the Akibarangers bid farewell to Hiroyo and Kozukozu, they disappear along with the three Sentai warrior ghosts.
- Biojet 2 (shared with Green and Blue)
- Super Electronic Holography
- Yellow Flash
- Mika is the first female Yellow Ranger and also first female Yellow Ranger did not wear a skirt in her suit.
- Her English dub name is Casey, which is also the name of the Red Ranger from Power Rangers Jungle Fury.
- She is also the first female Sentai Warrior to die.
- Mika was written off the script because Yuki Yajima left the show possibly out of pay issues, similar to Austin St. John, Walter Emanuel Jones, and the late Thuy Trang in the second season of Mighty Morphin' Power Rangers.
- For Mika's last episode, her voice was dubbed over by an uncredited Mayumi Tanaka as Yuki Yajima had only completed ADR for the first nine episodes before leaving abruptly.
- With Mika appearing as Yellow4 in her Akibaranger cameo, it confirms that she is still considered a Ranger even after death, even with her replacement as Yellow4 in all later appearances including the Legend War.
- Near the end of episode 10, Bio Robo's eyes glowed triggering her Bio Hologram to feature a footage of herself. The footage shown is her shot in the closing sequence.
- In the Philippine-English Dub in the series, Mika is voiced by Geraldine Oca.
- Jun Yabuki - The Sentai who temporarily replaced her as the Yellow4.
- Trini Kwan - The first female Yellow Ranger and first female Yellow Power Ranger to be replaced.
- Kendrix Morgan - First female Power Ranger to die while active as a ranger.