Why did snake just agree to wait 6 months?
Why didn't she just kill them and be over with it?
That's really out of character for me.
I believe (from reading the book) it was a combination of:
Sengoku had no real reason to want to kill to Araragi and co, it was basically just her getting carried away by the craziness of becoming an oddity and the despair she was feeling (it's not like she genuinely gave a shit about her feelings for Araragi or that killing him made sense)
Senjougahara mentioning graduation brought back some of Sengoku's humanity
Hearing Senjougahara speak, Sengoku had started to actually quite like her
It's enough to make her allow herself to accept the suggestion that a delay would make no difference
maybe if you really want to believe that. And in no way was she carried away. You don't just want to kill somebody because you got "carried away". These are just lame excuses.
Kuchinawa-san (i.e., herself) brings up how little sense it makes to kill Araragi. Her attitude to it is that "it can't be helped" as Nadeko (but not "watashi") was an oddity.
>Nadeko (but not "watashi") was an oddity
Kinda sucked that the subs translated all the "Nadeko"s as "me", even though one of her major character points is that "me" is different
>characters in Monogatari
She literally had zero fucks to give at that point. Killing Araragi was the only worthwhile thing she could do so it's not like there was any rush for it either.
Because Senjougahara told her how to best kill them (first Shinobu etc.) and because she was nice to her (she even thanked her proberly for that) Nadeko agreed to fullfill her resqued to wait for six month.
Accounting for her
mangaka tendenciesand the fact that she even pictured it as a climactic anime showdown shows how little else mattered at this point for her, so putting it off was actually very much in character for Nadeko.
I mean besides the flaws given by others its fair to say that she was on a power trip. She knew that once they were dead the trip was over and no one would pay attention anymore.