In a fanfiction, Kaien's daughter might be a key figure in bringing about a truce between the vampires and the vampire hunters. She could grow up with a deep understanding of both sides, having been exposed to the vampire world through her father's connection and the hunter world through her family's legacy. This would lead to her trying to bridge the gap between the two groups, facing many challenges along the way.
She could be a rebel. She might oppose the traditional ways of the vampire hunters or the vampires. For example, if she falls in love with a vampire when she is supposed to be a hunter, it would create a great conflict. This could lead to her being ostracized by her own group and having to find her own path.
One possible story could be that Kaien Cross's daughter discovers she has unique powers in the world of Vampire Knight. She might struggle to fit in among the vampires and humans, while also trying to understand her father's past and his connection to the vampire world.
The Jujutsu Kaisen manga is indeed ending. It's been a great run, but all good things must come to an end. The final chapters are bringing closure to the characters and story arcs.