Sebastian, being the efficient butler, would likely immediately take charge of the situation. He would ensure the girl gets proper medical attention if possible. He might also start investigating the circumstances around the accident, suspecting foul play as is often the case in the 'Black Butler' world.
The other servants in the Phantomhive household would react in different ways. Mey - Rin might be very emotional and worried, perhaps blaming herself for not being able to prevent it. Finny would be distraught and try to help in any way he can, like carrying the girl to safety. And Bardroy might be more practical, trying to figure out how to deal with the aftermath, such as dealing with the car and any witnesses.
Ciel, on the other hand, might be more initially concerned with how this event affects his own plans and standing. But as he realizes the severity of the girl's situation, he could show some empathy. He might use his resources to find out who was responsible for the accident, either to help the girl or to use the situation to his advantage in some way.
Edward would be extremely distraught. He might blame himself for not being there to protect Bella. He would likely stay by her side constantly, using his vampire abilities to try and heal her if possible. Alice, on the other hand, might have seen the accident coming in one of her visions but was unable to prevent it. She would be filled with guilt and would try to use her visions to figure out how to help Bella recover.
In the fanfic, the 'gets hit and sees red' situation might be a turning point. For example, if she was previously a meek character, this event could be the catalyst for her to stand up against oppression. Maybe she was hit by a bully or an antagonist, and seeing red means she's now ready to fight back, whether through physical means or by using her wits to outmaneuver her opponents.
Her friends would likely be very shocked and worried. Some might rush to the hospital immediately and stay by her side, constantly checking on her condition. For example, her best friend might be in tears and refuse to leave until they know Bella is out of danger.
The other characters' reactions would be diverse. Bakugo might initially be very confused and maybe even mock Midoriya a bit, but deep down he'd still see her as a rival. Uraraka would probably be very empathetic and quickly become a good friend to Midoriya in her new form, helping her with things like getting used to the new body. And All Might would be very supportive, seeing it as just another obstacle Midoriya has to overcome in her journey to become a great hero.
Some of the male characters might be a bit flustered around Naruto as a girl. For example, Kiba might act differently, not quite sure how to interact with her in this new form. Hinata, on the other hand, could become even more shy. She already had a crush on Naruto as a boy, and now with Naruto as a girl, her feelings could be even more complex. The Akatsuki members, if they were to encounter Naruto in her new form, might underestimate her at first. But Naruto, with her indomitable spirit, would soon show them that she's still a force to be reckoned with, regardless of gender. And the reactions of the characters would not only be about how they see Naruto, but also how Naruto's new form affects the power dynamics and relationships within the Naruto universe.
Fishlegs would be really concerned and would use his knowledge to try and help. He might look for herbs or remedies that could aid in Hiccup's recovery. Snotlout, on the other hand, might initially try to act tough but deep down he'd be just as worried. He might try to show off his strength by helping to carry Hiccup or something like that. And Tuffnut and Ruffnut would be their usual chaotic selves, but also very caring towards Hiccup in their own unique way. They could make jokes to try and cheer him up while he's in pain.
One possible plot twist could be that the girl, instead of being severely injured, discovers she has some sort of supernatural power as a result of the accident. Maybe she can now see the spirits of the dead more clearly, which ties into the dark and supernatural themes often present in 'Black Butler'.
Dumbledore would be a key figure in the reactions. If he believed in Snape's innocence, he would try to find a way to free Snape while also not alienating Harry. He might start his own investigation to uncover the truth. The other Hogwarts teachers would be in shock. Some might believe Harry is right, especially those who have always been a bit suspicious of Snape, while others would be outraged and demand an explanation from Harry.
Perhaps she starts to question the safety of her environment or the people around her. This could make her more cautious and observant, leading to her uncovering secrets or plots that were previously hidden. For example, she might realize that there are those who wish her harm and start to take steps to protect herself and those she cares about.
Sasuke might be extremely suspicious. He has a long - standing relationship with Orochimaru, and this sudden change would make him wonder if it's a new trick. He would keep a close eye on her to see if she's still the same threat.