She might be initially surprised. After all, it's an unexpected way to declare love. But then she could be flattered that Castle has such strong feelings for her that he expresses them even in his fictional writing.
Beckett may feel a bit embarrassed, especially if the fanfiction is shared among their friends or colleagues. But on the other hand, she could also be touched. It shows that Castle has been thinking about her in a romantic way and has put his feelings into his writing. She might then approach Castle to have a more in - depth conversation about his feelings and where they stand in their relationship.
One possible scenario could be a really emotional moment where Castle finally gathers the courage to express his deep feelings for Beckett through his fanfiction. Maybe he uses the stories he writes as a way to convey his love in a more creative and less intimidating way.
She could be hesitant. Given Spike's nature and their history, Buffy might not be sure if she can trust his feelings or her own response to them.
She might be really happy and excited. After all, it's great to have someone appreciate your creative work.
He could react with anger. After all, if he has feelings for Beckett, seeing her with someone else like Vaughn might make him furious. He might lash out at both Beckett and Vaughn without really understanding the situation.
Bulma might be a bit skeptical at first. Given Vegeta's tough exterior and past behavior, she may wonder if he really means it. But as he continues to show his sincerity, she would gradually accept his love and reciprocate it wholeheartedly. She might also start planning their future together right away, thinking about things like family and a more stable relationship.
In some fanfictions, Harley might react with shock and disbelief at first. She has been through so much with the Joker that she might not trust his words immediately.
He might react with jealousy. He could glare at Josh and then give Beckett a hurt look before storming off.
He might be overjoyed at first. Castle has always been deeply in love with Beckett, and a baby would be like a new adventure for them. He'd probably start making plans right away, thinking about baby names and how to turn one of the rooms in their place into a nursery.
She might try to manipulate Loki. Natasha is very good at getting into people's heads. She could play on Loki's ego or his own insecurities to gain an advantage. For example, she could pretend to be interested in his plans or offer to help him in some way, all while secretly planning her escape.
Hermione may first try to use magic to defend herself or escape right when the kidnapping is taking place. But if that fails, she will start to analyze the situation. She would think about what she knows of Dolohov from her studies and any previous encounters. Then, she would form a plan. She might even try to find allies within Dolohov's ranks if there are any who could be swayed, by appealing to their sense of self - preservation or better nature.