Mimi straight up gaslighting the readers by saying "ooooooh progresss" and by trying to make MC likable
As incredibly flawed and sometimes outright garbage as this manga is... she actually has a point.
And it's the reason I started following rent a girlfriend in the first place.
Yes, Kazuya is a total doormat. But, compared to most harem MCs, he's a doormat with a clear goal. From the beginning, he has had his eyes set on Chizuru and he has stuck with that. A lot of the putting up with other girls (fake dating Ruka for example) was in order to work towards that ultimate goal.
In fact the entire "trial period" thing with Ruka... they never go on dates or really spend time together - it's pretty much her stubborn refusal to take no for an answer, while he seems to think of her as a friend and doesn't want to hurt her.
The only real deviations he makes are when Mami is involved, and she has (or at least had) emotional leverage on him, not to mention the attempts at blackmail.
But he has moved past Mami - she no longer has emotional leverage, nor does she have the capacity to blackmail him anymore.
Ruka was never a real obstacle in the first place, and Mini - as we see here - is 100% on board with him and Chizuru.
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The underlying issue with this series is the absolutely fucking GLACIAL pace, but there is consistent progress in it. At regular intervals we see steps forward in the relationship between Kazuya and Chizuru; it's just easy to overlook them because of the horrible amounts of filler that happen between those events.
Similarly, that extended period of nothing of note happening causes negative traits to be exagerated, while positive ones are understated.
HAVING SAID ALL THAT NONSENSE
The only reason this manga is still readable is Mini being an absolute gremlin who seems to be as fed up with the lack of progress as we the audience are.
Mini... is us. And she always has been.