Yes. Billy Russo is indeed a character in the Punisher comics. He has a significant impact on the overall narrative and the development of the Punisher's story.
Billy Russo in the Punisher comics is a villain. He has a troubled past and a deep-seated grudge against the hero. His actions drive much of the conflict in the story.
One great 'Billy Russo Punisher' fan fiction is 'The Redemption of Billy Russo'. It delves deep into his character, exploring his complex psyche and his relationship with the Punisher in a really interesting way.
You can find 'Billy Russo Punisher' fan fiction on various fan - fiction websites such as Archive of Our Own (AO3). There are tons of stories there, just search for 'Billy Russo' and 'Punisher' in the search bar, and you'll get a long list of relevant fan fictions.
The Punisher, or Frank Castle, was a normal guy with a family. His military background gave him a set of skills that were both useful and deadly. Once his family was massacred, he snapped. He turned his skills towards punishing those who he thought deserved it. His origin story is one of tragedy and a thirst for justice outside the normal bounds. He doesn't wear a colorful costume like some superheroes. Instead, he has a simple skull emblem on his chest, representing death to those who do wrong.
Krista's significance in 'Attack on Titan' lies in her ability to surprise the audience with her hidden identity and her growth throughout the story. Eren, on the other hand, is crucial as he is the catalyst for many of the major events. His relationship with Krista is part of the web of character interactions that make the story so engaging. They both contribute to the overall theme of survival and the exploration of the truth about the Titans. Krista's character arc is also linked to the broader political and social aspects of the story, just like Eren's actions are tied to the fight against the Titans.
I'm not sure specifically which 'Krista Allen frat boys story' you are referring to. There could be many stories involving her and frat boys. Maybe it could be about her experiences with frat boys in a social or collegiate setting, but without more context, it's hard to say exactly.