Yuki Yajima’s departure from Bioman is a controversial issue. We don’t know why she left. We all get different stories and reasons from different sources.
From what we can tell is that it might have been abrupt. In her last episode. She isn’t seen at all. She is in her suit the whole time, and that might not have been her voice. Her death episode is glorified by a lot of fans, but for me it’s pretty abrupt and out of nowhere. It does introduce the Anti-Bioparticles, and it’s nice that the team didn’t immediately recover from it, but her death episode reminds me of how Poochie was killed off on “The Itchy and Scratchy Show” on the Simpsons.
Yuki Yajima has been off the radar ever since. There are many fan theories:
Contract disputes: Contracts are really important, and if it is not followed, an actor may leave.
Pay disputes: Same with contracts. There must be a reasonable pay that is negotiated. An actor can leave if the pay isn’t fair, or if they think they deserve more.
She’s pregnant: You can be with child while filming most TV shows, and they can adapt to that, by writing it in, adjusting the camera angles, or just saying that your character got fat. But, if you’re doing an action show, it’s not wise to do stunts when you’re preggers. And if you’re playing the more action oriented woman on a TV series (I’m not saying Hikaru didn’t do stunts, I’m saying that Mika and Jun were the action girls on the team, so their actresses had a lot more stunts to do) and don’t plan on getting rid of your baby, it’s not wise to jump on top of cars and duel with Farrah Cat.
She just quit: It’s hard working on a tokusatsu show. Like I said above, you do a lot of stunts, it can be cold since you work outside a lot. You have to go to work early, and leave work late. You might have a lot of fans bugging you as well, and it’s hard to live up to this idol standard. This can be hard for actors and actresses, and makes one question if they truly want to be in the business.
Another example of this is the departure of Yuriko Shiratori (Hana) from Kamen Rider Den-o. In the show, her character is affected by Yuto using his Zero cards (I think) and de-ages into a ten-year old, after she is missing from the train, after new train tracks are seen being built. Fortunately she retains her memories, and her maturity, so essentially she is a young adult trapped inside a child’s body. She still can kick the Taros’s butts, and she still treats Ryotaro like her little brother. Tamaki Matsumoto was able to pull this off. Originally people thought that she was a scrappy, but in the sequel movies, she gradually becomes more of a badass. This breaks, however, pretty much every law and role of time travel, and the rules that existed in Den-o’s world . Hana is a singularity point, and should not be affected by changes in time, yet she physically de-ages due to changes in her own time, and future. Breaking an in-universe rule shows that this was not planned, and Yuriko Shiratori’s departure remains a mystery along with Yuki Yajima’s.