Well, it might be a combination of factors. Maybe it was the negligence of someone who was supposed to protect her, or a series of unfortunate events that led to her demise. It's hard to pinpoint just one person as being solely responsible.
It's possible that it was the main character's decision or mistake that ultimately led to the girl's death. But we'd have to look at all the circumstances and characters involved to be sure.
The person behind the death of the 5 children in the FNAF story was a man in a purple suit. He lured the children into a back room at Freddy Fazbear's Pizza and committed the heinous act. His identity remains somewhat of a mystery, but his actions set off the chain of events that led to the animatronics being haunted by the children's spirits.
In some versions, it could be a former ally who has been corrupted. This character, once on Ahsoka's side, has now turned against her due to some external influence or personal greed. Their knowledge of Ahsoka's strengths and weaknesses would make them a formidable opponent, and they could be the one to cause her death.
The comic doesn't explicitly point to a particular individual as the one who killed Kurt Cobain. It keeps you guessing and leaves room for your own interpretation.
Another character in the novel is responsible for Mason Verger's death.
Teng Zijing's death had a certain connection to Fan Xian. Teng Zijing had died to protect Fan Xian. In the play, Teng Zijing and Fan Xian established a deep friendship. They helped each other and influenced each other. Teng Zijing was Fan Xian's refuge, and Fan Xian was Teng Zijing's guide. However, in the Niulan Street assassination case, Teng Zijing sacrificed himself to protect him and was eventually killed by Cheng Jushu. For revenge, Fan Xian defeated Cheng Jushu and told Teng Zijing's wife and children about it, providing them with burial fees. Therefore, Fan Xian bore a certain responsibility for Teng Zijing's death. In order to protect Teng Zijing, he personally put Guo Baokun's sack on him and took all the responsibility on himself. Fan Xian's actions showed his deep friendship and sense of responsibility for Teng Zijing.
It could be the enemy forces. In a war novel, the most straightforward reason for a character's death is often combat with the opposing side. They might have had a strategic advantage or just been more numerous during the battle.
Christine herself might be responsible in an indirect way. If she rejects the Phantom completely and coldly, it could shatter his already fragile mental state. He might then take his own life because he feels there is no purpose left for him without her love. So, while she doesn't directly kill him, her actions lead to his death.
In the graphic novel, it's suggested that a combination of factors and individuals might have played a role, but no single clear culprit is pointed out.
In the movie Search, Rachel was not responsible for Ye Lanqiu's death. Ye Lanqiu committed suicide because she had a mental illness. However, Rachel was not involved in her treatment process and did not make any decisions or instructions for her actions. Therefore, she was not responsible. However, in the movie, Rachel also expressed her grief and reflection on Ye Lanqiu's death, which reflected her concern and love for her patients as a doctor. It was commendable.
A new villain could be introduced in the fanfic who is specifically out to get Connor Kenway. This villain might have a personal grudge against Connor or be on a mission to eliminate all the Assassins, and Connor becomes their prime target and ultimately falls to their schemes.