That someone can read this story and think that Fuuko is some sort of hero is still a mystery for me. She is clearly mentally sick.
Yuni will without doubt cheat again. She did not even say that she was sorry, and she kissed Fuuko seconds before Nanase arrived. She really is the worst. Her only redeeming feature is that she clearly is mentally sick as well and therefore her actions is more due to her issues then any malicious intentions.
Nanase has no spine and is the architect of her own future misfortune.
I agree. It astonished me that Fuuko had so much supporters, because people think that Nanase is a horrible girlfriend (there is some truth to this). But they also forgot that the only reason why Fuuko knew things about them is because she is super obsessed with Yuno and stalked her. To the point where she shows up uninvited to places that she knew Yuni and Nanase would be, or in the another case shows up to places that Yuni expected Nanase.
Additionally, she took advantage of Yuno's mental state and easily manipulated her into cheating. Now I'm not saying Yuno is innocent, cheating takes two people. And although Yuno was coerced (I say this because Fuuko basically bothered her everyday until she gave in), Yuno also eventually gave in to the desire of having a relationship where she gets attention (something she lacked and wanted with Nanase).
To me, Fuuko is not likable nor a hero (as you mentioned). She quite literally took advantage of a situation from a person she stalked and is obsessed with. Then throws a fit when she finds out that she was only a side-piece for attention and comfort (even though she tells Yuni all the time about how she's okay with being the number two girl. But I feel that's just a manipulation tactic to make Yuni feel more okay about cheating as long as Nanase is branded as "number 1 girl"). Fuuko is unlikable and creepy.
I think a main reason for supporting Fuuko, at least for me, is because this isn't the type of manga that's supposed tie up neatly and have people act rationally. The author pretty much writes so that you're in support of the cheating. It's the drama. Everyone pretty much acts passively and reactively except for Fuuko.
Fuuko definitely isn't a good person. She's manipulative and obsessive. But it's fun to cheer for the things she does to bend everything to her liking. There's this je ne sais quoi about her ya know. If any character had shared any one trait of hers, I'd most likely dislike them. Putting them together? Let's fucking gooo
