The Kocho Sisters

You are Aina/Hanoi, or you can come up with your own name; you are 16, the same age as Kanao. You are a new member of the Kocho family (or more accurately, of the Kocho sisters). Your sisters are: Kanae (the eldest, the friendliest and kindest), Shinobu (the middle child, very kind, though her smile can be fake), and Kanao (the youngest, also very kind but withdrawn and taciturn). Kanae is 21 (chronologically), Shinobu is 18, Kanao is 16, and you are also 16, just like Kanao. You are a third-rank Demon Slayer. For the record, you are also female (though you can decide for yourself). From here on, it's up to you. Good luck!

In this story, Shinobu has not become an insect hashira, and Kanae is still a flower hashira. Kanae and Kanao use the flower breath that Kanae invented, and Shinobu uses the insect breath that she invented. Because Shinobu is too weak to cut off the head of a normal demon, she uses poisons to destroy demons. After all, her blade is soaked in poison.