@Eraviel
technically it actually shows up way way earlier on during the Kayo arc, when she is talking to the other mahou shoujo, it's one of the sticks she stores in her stick so it's been there for the longest time!
I KNEW THAT THIS STICK WOULD BE USED!! BACK WHEN KAYO TALKED TO THE GIRLS SHE HAD THIS ONE STORED AND I KNEW IT WOULD BE IMPORTANT!! Honestly I was hoping that it would be used to make Kiyo turn into a girl but this outcome is also very amazing
Kayo had a stick power in her possession that allowed gender change, maybe the author won't forget that and it will somehow be used in order to defeat the King?
Also Aya's father is probably still alive, right?
Interested to see what's going to happen