I finally came here. So, it started back in 2012?.. Uhuh, I see...
Actually, if I look closely, it's not so sadistic.
It's a story about a girl who is in love with her senpai. She even won the competition the previous day because she knew he was watching her. Even though he doesn't like crowded places, he came, so she gave it all she got to win.
And now he called her to confess, presumably, so she is looking forward to it. She rejected a lot of confessions already, including ones from popular guys, because she wants to go out with her senpai. She teases him a bit, with a smile on her face, but actually she wants to hear that confession. Because she is in love with him.
But of course he starts to mumble, hides his eyes and gets all red. Because it's her senpai. But she urges him to say it out properly. This "you can do it~" is loveable. She wants to hear a proper confession. She even speaks it out for him, giving an template, so that all what's left to him is to repeat.
And this line, "senpai confessing to me, impossible"...it reminds me of some small children, who secretly want a popular toy, but speak out loudly "my parents buying it for me? Absurd! It's ridiculously expensive, no way they would pay so much! And it's also stupidly popular, all my classmates have it! If I come in class having this toy, I will look like I'm sheep in the herd!". This kind of cute childish tsundere self-rejection.
And to see that the person she loves doesn't have guts to confess to her properly...I bet it hurts a lot. I wonder, how could any other girl react on her place. Maybe run away, crying.
Nagatoro reminds her senpai everything. All the things for which she got hurt in the past. How other girls mock him in school, how he is a little creepy. She has already been calling him gross for some time, from time to time, because she doesn't like it. She wants her loved one to be flawless. She doesn't want him to be badmouthed. Because it hurts her a lot, maybe even more than him himself.
And seeing his reaction, she goes wild. Here it "rubs the wrong way" even me a little, with all these insect comparisons. But still, how she demands him to look her in the eyes, how she grabs him and doesn't let him to run away...
But the most of it all, how she starts crying on 43. Seeing that the person she loves is so weak, she wishes for him to die...strangely, I understand it.
And the rest, after confession, all this familiar tsundere-ish bittersweet routine. Argumenting accepting to go out with him, giving him a handkerchief...
Wholesome. Understandeable. Makes feel.
Oh, so, "going home with ... №1" consists of only 1 page, huh.
I don't like it being done as POV. When we have to guess how her senpai mumbled his confession in the first half.
I like how some details got into serialization unchanged. Her participating in swimming, her senpai being tall, shaggy, skinny and pale. She even mentions that he draws. Yep, it really gives an impression that serialized version will end with this scene. Maybe next summer, when they will be in 3rd and 2nd grade respectively.
Oops, I made an essay. To revise it will be a pain...
TL;DR: She is not as cruel as you think. She loves him much more than you think. She wants him to not be pathetic, more than everyone else. She can be forgiven.