I read the last few pages of this topic, and I also read some discussions about Ichigo 100% on another forum. It seems like many people don't understand the ending, why Nishino won even though the story was originally set up for Toujou. Some say it was the result of of a fan poll. I don't think that's the case, it's just that story-wise, it was more natural this way. Let me explain.
When Ichigo 100 % started, its basic plot ("OMG, without glasses Toujou is beautiful") was
very cliché and wasn't enough to last more than 20 chapters. If it had failed (like Ane Doki), it would have been enough for a very decent Toujou ending within such a short frame.
But it was quite funny, so it was popular enough to last. Every reader knew that a Toujou ending was a sure thing, and the glasses thing was already dying. So the author introduced another girl, Satsuki, trying to seduce Manaka. That way he would be conflicted about who to choose.
First problem: how could Manaka openly flirt with two other girls, even though he had a titular girlfriend? Nishino was sent to another high school, and after a long time of Manaka being a jerk, Nishino finally broke up with him.
Second problem: how could Satsuki compete with Toujou? It was like Toujou/Nishino: everybody knew that Toujou was supposed to win, the only difference was that Manaka didn't have to worry about taking the initiative of breaking up with someone. There was even less suspense, and as a result, no plot.
When Toujou learned that Manaka and Nishino had broken up, the manga was as good as finished. Toujou and Manaka didn't have any obstacle to confess, they were already almost lovey dovey, and they even had a movie date (when they met Misuzu). But it was still popular enough, so it had to go on, and the author had to find a way to make this interesting.
That's when Nishino is reintroduced. Toujou and Nishino's feelings are very well known to the reader, they are completely in love with Manaka. But Nishino, as the ex-girlfriend, could be a question mark. What does she think about Manaka now? Is she so casual with him because she found a new love?
From that point, the relationship between Manaka and Toujou remained exactly the same for the next 90 chapters: they share some special moments from time to time, but there was no confession, the only thing that lacked in their relationship. So there was no progress at all during a long time. Satsuki wasn't even relevant anymore.
But the author had a great opportunity with Nishino, she could create a new relationship step by step, not from scratch, but from a damaged one. Only hints were given to us about Nishino's feelings, sometimes contradictory, like when she told him she was planning to go to Paris (leaving him without her). Nishino then became the only dynamic thing in this manga, she was the plot.
During the 3 days perfect trip with Manaka, we finally learned that she was planning to get back with him. She was the one taking initiatives, but she never forced him unlike Satsuki. In the same time, Toujou did nothing, because doing something would instantly mean the end of the manga.
The first turning point was in chapter 135. Toujou then had the perfect opportunity to confess, the mood was great, they were alone, Manaka was waiting for it... But she instead told him she was planning to go to a different university. Even with the filmed confession, this trip ended with "maybe she does love me" for Manaka, when it should have been "I'm glad she loves me".
Honestly, that was for Toujou the biggest mistake of her life (even Misuzu told her before to tell him about the university
after confessing). Now, Nishino was the one with all the momentum. She did confess, when Toujou was dumb enough to accept someone else as her date at the love sanctuary. Now the whole story was about the growing love between Manaka and Nishino, unlike at the beginning. It's how Toujou became history for Manaka, and it would have felt unnatural if he had chosen her even though he had no problem letting things stall between them for so long. The second turning point was in chapter 153, it cemented the fact that Toujou had already lost.
So if she lost, it's because the plot needed some expansion, and all her cards (possible mysteries about her) were already played.
Ichigo 100 % in a graph: