
We all have our own likes and dislikes and this time I'm not even concerned as to whether or not she's a love rival. Her extremely cocky, "I'm better than you until you prove otherwise" attitude and the way she addresses (or doesn't) her senpai is extraordinarily disrespectful, particularly in Japanese society.

well, japanese people take as disrespectful the wrong use of honorifics. But it's based on merit and seniority. As she applies it it can be seen as correct since she proves it through testing their skills.
A genuinely disrespectful way would be if after winning against Ayumu, she'd address him as "kun" or lower. Instead she still regards him as upperclassman but with near equal footing on skills (leaning more towards her) so she chose "san".

Seems you're intent on defending her regardless of her actions/inactions. You really think winning just one game of shogi is enough for her to claim ultimate seniority over Ayumu and disdainfully expect him to call her senpai? Bullshit.
And how about the disrespect that she showed the Prez by not addressing her as president until she got her ass whipped. Conceited little fuck needs to get taken down quite a few pegs. Just thinking about her makes me wanna drop this series and rate it a big fat zero.

woah ok, my intent is not to "defend" the new char, but to point that so far at least it doesn't pose any negative point on the series. But I think I'm talking to a brick if you are telling me you think it's fine to rate bad a series that did so well just because of a character that was just introduced 70 chapters later.
To me, her addition to the cast just pave the ground to what will the shogi club become. Since the author has dropped a couple of times sempai's graduation and the impending disband of the club for lack of freshmen interest in it. Her gutsy attitude, which you take as rude and conceited, as I see it, is a trait that might make her a really good club prez, and if I may say so, even better than our beloved shogi sempai.

I know I wasn't here for the argument but I read your whole battle and I agree with all your points. having this new char make the story (to me at least) feel more realistic and not to mention I am sure she will character development to make her more likable later on and if not then that only make our president more likable. ( also in general if you read manga or watch anime I am sure you've heard of or seen the overbearing/cocky character trope.) it happens.

Well, I guess you can find stories like that. But I think this author's intent is to show the big picture of their social circles albeit subtly. ehm, like Komi-san which focus on everyone making friends even when all are so different. Even when he only focus on the main cast in the beginning, you can see how he make those additions enhancing the progression of time in the story. Idk, this might even mean the clousure for Shogi senpai series is drawing near :o
My enjoyment of the series has dropped by at least 50% in 2 chapters. If she's gonna be in every chapter, it won't be fun to read anymore.