One possibility could be that they meet in a dark alley in Gotham. Red Hood is on a mission to take down some low - level criminals when he stumbles upon Catherine Todd. She might be in danger, and he steps in to protect her. This encounter could lead to a series of events where they form an unlikely alliance.
Maybe Catherine Todd is a journalist in this fanfiction. She's investigating a story related to the criminal underworld that Red Hood is also involved in, though from a different perspective. Their meeting could be a chance encounter at a crime scene. They then start to work together, sharing information, and in the process, they develop a romantic relationship.
I'm not sure specifically what a 'catherine cell' is in this context as the term is rather unclear. It could be a very specific or made - up concept within that particular story.
Perhaps Todd is a normal villager who has always been fascinated by Naruto. One day, he discovers that he has some latent ability that is related to the Kyuubi's power. Naruto, as a sennin, takes notice of Todd and decides to train him. So, Todd could be an underdog character who is thrust into the world of ninjas and the Kyuubi's mystery.
In the 'the black widow the catherine nevin story', Catherine Nevin was probably a person who had actions or a reputation that earned her the 'black widow' title. This could mean she was involved in activities that were not above board. It could be related to financial misdeeds, or actions that took advantage of people's vulnerabilities. Maybe she was at the center of a scandal or a criminal case where her actions were so notable that she became known as the 'black widow' in this particular story.
I don't have enough information to say exactly who Todd James Pierce is in this context. He could be the author, and perhaps the stories are based on his own experiences or observations in Australia.
It could be a mysterious stranger she meets by chance. Maybe at a coffee shop, a guy who strikes up a conversation with her and shows an immediate interest in her life. He could be charming and different from Steve, which draws Catherine to him.
In the context of this fanfic, Catherine Rollins and Steve are likely characters created by the fanfic author. They could be original characters, or they might be based on existing characters from a particular show, movie, or book. Without more context, it's hard to say exactly who they are other than two individuals whose relationship is central to the story where Catherine makes Steve cry.
Sweeney Todd is a fictional character. He is the main character in a famous musical and various adaptations. There is no historical evidence to suggest that a real 'Sweeney Todd' committed the grisly murders as depicted in the story.