The characters would be devastated. Kurt, being one of her closest friends, would probably be in shock at first. He might go through a period of denial, thinking it's all a cruel joke. Then he would break down and cry, remembering all the times they shared together, from their fashion debates to their duets. He would likely be the one to organize a proper memorial for her, making sure it was as grand as Rachel would have wanted.
Quinn would also be deeply affected. Despite their past rivalries, they had grown to respect each other. Quinn would be one of the ones to try and hold the Glee club together during this difficult time. She would encourage the other members to keep their spirits up and remember Rachel through their music. She might also find herself reflecting on her own life and how Rachel's death made her realize the importance of living life to the fullest.
Finn would be completely heartbroken. He and Rachel had a complex relationship. He might blame himself, thinking that if he had been more protective or had told her how much he really loved her one more time, she wouldn't have died. He would withdraw from the Glee club for a while, not being able to bear the thought of singing without her. Eventually, he would come back, but always with a sense of sadness in his eyes.
Mr. Schuester would be in shock. He saw Rachel as one of his star pupils and a driving force in the Glee club. He would struggle with the guilt of not being able to protect her. He would try to keep the club going as a way to honor her memory, but it would be very difficult for him. He might also start a scholarship fund in Rachel's name for future Glee club members.
Mr. Schuester could be disappointed. He always saw Finn and Rachel as a power couple in the Glee club, their relationship inspiring others. He might try to mediate between them at first, but if that fails, he would hope they could both still contribute positively to the club despite the break - up.
Naruto would be extremely devastated. He sees Kakashi as a mentor and father figure. He might go into a period of deep depression at first, but then turn his grief into motivation to become stronger. Sakura would also be very sad and might focus more on her medical skills, vowing to save more lives in Kakashi's memory. Sasuke might have a more internal reaction, feeling guilty if Kakashi died protecting him, and it could further fuel his own goals, whatever they may be at that time.
The Weasley family would also be greatly affected. Mrs. Weasley would surely mourn Harry as one of her own. Ginny, who had feelings for Harry, would be heartbroken. She might become more fierce in her pursuit of justice in the wizarding world. And the other students at Hogwarts, like Neville, would be inspired by Harry's sacrifice to step up and be braver in the face of danger.
Winry would be heartbroken. She loves Edward deeply. She might initially go into denial and then be filled with anger at the circumstances that led to his death. She could also turn her grief into a determination to help others with her mechanical skills, in memory of Edward.
Sasuke would be deeply affected. He and Naruto had a complex relationship. He might feel a sense of regret for all the times he had pushed Naruto away. His reaction could range from anger at the situation to a new - found respect for Naruto's sacrifice.
Ruby would be devastated. Qrow is her uncle and has been an important figure in her life. She might initially go into denial and then be filled with rage, vowing to avenge his death. She could become more determined than ever to take down Salem, seeing it as the only way to make his sacrifice meaningful.
Hermione would likely be devastated. She might go into a deep state of mourning, but also use her intelligence to try and figure out what led to Harry's death. Ron would be angry and heartbroken at the same time. He'd probably want to seek revenge if there was someone or something responsible.
Lucy would be completely devastated. She and Natsu have a very close bond. She might go into a deep depression, constantly blaming herself for not being able to save him. Gray would be angry at first, feeling like he should have been there to help Natsu. Then he'd be sad and would probably vow to avenge Natsu. Erza would be strong on the outside but inside she'd be broken. She might try to keep Fairy Tail together in Natsu's memory. Happy would be inconsolable, constantly flying around looking for Natsu and refusing to believe he's really gone.
Well, some characters' reactions can be really complex. For example, Dumbledore's portrait might show a solemn look, as if he knew this was an inevitable outcome. The students at Hogwarts would be in a state of shock. Those who were in Slytherin house might feel a sense of loss for their head of house, even if they didn't always understand him. And Neville, he might see Snape's death as a tragic end to a misunderstood hero.