>>134511

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>>134513

Well, obviously Sora doesn't know about his sister's job beforehand, because she's hiding it, which she does because it's illegal.

As for why Sensei didn't mention his sister in the video... well, what point would it serve? So that they could talk about it beforehand? Would it necessarily be a good thing (for Sensei)? As they might end up talking each other out if it. Even as it was, sister tried to talk Sora out of it, but since they were already both excited in the heat of the moment they ended up going along. But it could've been different if they were given plenty of time to ponder and discuss it in the comfort of their home.

Besides, we know Sensei expects Sora to apply for death, but we don't know if she knows the exact method of death he would request. And if she doesn't then for her there's no point to introduce his sister as her assistant at this point, when for all she knows the said assistant might not even end up being involved.

And the out-of-story reason is that having it be as it is makes a better and hotter story flow with sister's involvement being a surprise like this. If sister's involvement would be revealed in the video, before we even meet her in the story, it wouldn't hit as hard, because to us she'd be just a new random character being introduced. The way it is, she's introduced as Sora's caring older sister, and the whole exchange where she cluelessly checks in on him while he's secretly masturbating to his upcoming death is hot. And then the surprise reveal of her being Sensei's assistant is hot because we didn't expect the same caring older sister to also be a beheader, and it's hot that she's gonna behead the little brother she was just shown to care about. This dynamic wouldn't have worked if she was introduced as a beheader right away.