Kanata does drop a few hints to explain her behavior, although those hints are scarce and pretty cryptic.
After the disciplinary committee meeting that ends in a brawl, Kanata approaches Riki, saying that the distribution of happiness in the world is a zero sum game. If someone is happy someone else must be sad
Kanata loses her composure when the flyers appear, twice. The second time after Riki confessed and the rumors keep spreading, Kanata almost screws up her act and calls Haruka just by her first name while confronting her in the courtyard. When Haruka leaves, she tells Riki “She’s going to destroy herself, that girl.” She mocks Riki for assuming she’s trying to destroy Haruka. She says her goal is the exact opposite.
“I’m not chasing her out to destroy her. Rather, if I don’t do it, she will be broken.” She believes she’ll be happier that way. “Next one… It will have to be the next place where Haruka Saigusa finds her place in the world.”
“I’m a bully. Just like you’ve said so many times.” (they’re translating ‘Hitodenashi’ as ‘Bully’ again)
“I’m a bully… therefore I can do whatever needs to be done. But, Riki Naoe, you are also a bad person. And because of that, I hate you.”
“I’m not crazy about you either.”
“Oh, then it seems we match. Hmm? Why don’t you give up on Haruka Saigusa and go out with me instead?” “Oh dear. I was rejected. Well then, this heartbroken maiden will just take her leave.”
- Rain scene bad ending.
(Sorry, @Kanon, for bringing it up after all)
Kanata, disguised as Haruka, reveals her identity.
Riki blames her for “snatching it all away” from Haruka.
“I told you before, didn’t I? My reason. That if I didn’t do this, that child would be broken.”
She casts away her disguise and lectures Riki on happiness and negatives. That some people aren’t given a place to exist.That Haruka is one of those who always gets all the bad things. That she cannot be saved by anyone. But maintaining the status quo is enough.
"She held that hatred tight, and kept looking ahead… And maybe that way she was able to find a little bit of happiness.
Riki’s narcolepsy kicked in. Kanata’s voice is the last thing he heard.
"…Don’t get close to Haruka Saigusa. You can’t save that girl. You can’t even recognize her. Just by losing one thing, that girl gives up… She’s that kind of person. I’d rather not smell that stench of blood anymore. I don’t want to see that flower of blood on the asphalt. So, stay away from her… Don’t ever get close to her again."
If you pick the right choice and get the non-bad ending rain scene, Haruka tells Kanata to die and comes really close to attacking her with a pair of scissors. Kanata gets mad over how Haruka is acting like a victim.
Then Kanata gets mad at Riki for asking about her reasons all the time, but she explains. “If I take away everything she grasps onto, she’ll finally be forced to revert.”
- Finally, during the last confrontation and Kanata’s confession:
Kanata is eventually prepared to spill the beans, but gives Haruka one last warning:
“If you find out, you won’t be able to go on like you have until now.”
Then she tells her part of the story:
"If it turned out that neither of us was appropriate to be the heir, they had no use for either of the twins… that’s what they told me."
They promised her everything as long as she would hate Haruka. She refused everything. Then they threatened to make her ‘like Haruka’. Little Kanata couldn’t oppose them, then. She was too afraid. "‘One of you needs to be culled,’ they said."
If she didn’t hate Haruka, Haruka would be killed.
"If I didn’t… Haruka would… Haruka would disappear…"
Therefore, she can’t help her. Therefore, she cannot allow herself to be helped by her.
Summing it up:
a. For Kanata, it’s a universal law that Haruka will always get the short end of the stick and cannot be saved. (Because she’s bad at everything ?).
b. Haruka’s actions will eventually backfire and destroy her
c. Kanata believes she must take away the places Haruka wants to belong to right now, so that she will find the ‘next’ one where she actually belongs. Also, she would be "forced to revert"
d. That by holding on to her hatred, Haruka could keep going and maybe even find a little bit of happiness. Therefore, the “Status quo” should be maintained
e. Just by losing one thing, Haruka gives up… She’s that kind of person. In this case, it ends with suicide.
f. The family threatened to kill one of the twins if Kanata didn’t hate Haruka.
Ok, so those were the hints. Here’s my interpretation:
Back after my first playthrough, I was convinced that Kanata deliberately played the villain so that Haruka could support herself with hatred. I forgot why but I guess it’s because Kanata pretty much said so in the rain scene bad ending.
How was the conflict of this route resolved? By Haruka accepting that she doesn’t need a person to blame for what’s happening. That’s her achievement, something she learned after numerous trials. She broke free from the teachings of her family, which blamed EVERYTHING BAD on Haruka. Now imagine Haruka, before learning to not blame bad things on people, coming to the conclusion that her sister is actually a great person. Remember that Haruka made it something like her life goal to sabotage Kanata and became a troublemaker for that reason. What would happen? If Haruka can’t blame Kanata for everything, she would blame herself instead. And the obvious conclusion to that would be suicide. That’s why Kanata went out of her way to be extra bitchy. It explains Kanata’s final warning, and why she gave in when Haruka decided to stop the blame game.
Then there’s the part about Kanata “taking away” things from Haruka. Things like her classmates’ favor, the school, Riki, the bench, and AHEM, the maintnance committee. I believe that Kanata wants to take those away before Haruka gets REALLY attached to them, because she could lose them easily. This fits with the “protecting from family” interpretation that’s been mentioned here several times. As long as Haruka is still in that school, she is within the family’s grasp. Even if they don’t attack her directly, they could easily sabotage her school life if they wanted to by flexing their power muscles or simply ordering Kanata to. The more attached Haruka grows to the things she’ll lose, the more she will suffer. It could even end tragically. Therefore, it would be better for Haruka to go somewhere else. ALTERNATIVELY, if we leave the family out of the equation, according to the universal law that Haruka will always suffer, she will ultimately lose the things she gets attached to.
Kanata’s methods sure are awkward, rough, and over-the-top. They also add to her feelings of guilt…
phew. That was a piece of work