Responses
I think she was from long long time ago. During War kind of time. Where there're bom flying everywhere, that's why she was scared of firework which sounds loud.
And explained why she is so good with the toy gun at that festival.
If your right, then her wish of killing Nagisa won't be fulfilled 'cause Nagisa already died of old age.
I think sakuya-chan is a dog in her past life.. lol because she is afraid of fireworks.. or maybe a cat because she easelly sneaks in and out to hina chans bedroom.. XD