You are probably right that this was the best outcome for everyone involved though Since the chaotic element was introduced into the "equation" as you say, it was all going to go to shit one way or another anyway. Why characters like Fuuko are always depicted so assholish in these stories, reveling in it all, I am not sure. Makes me think she probably does not truly care about Yuni, but it's not like we have ever gotten a real good look inside her head.
I was observing Fuuko very carefully, exactly looking for those "signals", is she sincere or not to Yuni, and I did not find any. Except a little evil smile, but it's given to Nanase catching her kissing Yuni
People call her a stalker, but I found that she was following Yuni at least 3 or 4 months before she discovered her real ID (it's info about anniversary)
So, I suspected she fell in love with an unknown girl who is venting and having troubles with a girlfriend. And as an opportunist, Fuuko decided to "help". She takes her chance being fed up with falling for straight girls.
People call her a blackmailer. Really? She never used anything against Yuni, and there are a few very compromising pics, including all posts on her venting account
Sexual harassment? Manipulation? In Osaka, when Yuni licked her wounded ear, Fuuko moved from her saying "We can't..."
it was YUNI who initiated sex
Every time when she speaks about Yuni, or to Yuni, she looks adorable and very sincere. I would be very disappointed if author suddenly turns to some unknown dark side of Fuuko. She is the most noble villain in my life and I almost wish that she is real...
Actually, I wish all those girls are real, but Fuuko, she is so special as she is now. I really like such passionate and brave characters with flaws that make them feel very real.
I think, if there's possibility that Fuuko does not truly care about Yuni, it would be very unreal according to the story until now, when story is in a state of finalization
She had so many chances to destroy everything, literally annihilate both Yuni and Nanase 10 000 times
I think she really cares about Yuni, from everything I see until now.
It sounds like you're ignoring Fuuko's bad personality because you don't want it to true. She's clearly written to be a villain, even if she has some sympathetic aspects to her.
The blackmail here is very clear and fits the literal definition. Fuuko snapped a picture of them kissing and used the threat of revealing it to coerce Yuni into being by her side. Later, she even says, "Do you want it to spread? That you're cheating on your girlfriend with me." Blackmail isn't the act of revealing the compromising information. It's the demand of something in exchange for not doing so.
I'm not going to cite an example for each point, but Fuuko's dark and possessive personality isn't exactly a secret. This very chapter, she goes out of her way to destroy the remaining relationship between Yuni and Nanase after Yuni explicitly tells her not to if she cares about her. She certainly didn't respect Yuni enough to follow her wishes.
I'm all for rooting for Fuuko even if I don't like her, but please let's not pretend she is a saint lol.