The Silver Flame is surely a main character. There could also be characters related to the Silver Flame, like their comrades or mentors who might have influenced their growth and abilities, which in turn helped them to defeat the top huntsman. And of course, the top huntsman is a key character as the one being defeated.
In the fanfic, the Silver Flame could be representing an underdog force. Their victory over the top huntsman might symbolize the triumph of the underestimated. They could have used their wits and the element of surprise. For example, they might have feigned weakness at first to make the top huntsman overconfident, and then launched a sudden and powerful counter - attack using their unique skills and abilities.
Ruby could be a great main character for a 'rwby silver flame fanfic'. Given her natural leadership and combat skills, she could be on a quest to understand and control the Silver Flame, perhaps believing it could be a new weapon against Salem.
I'm not sure as I haven't read it, but likely there will be a Huntsman as one of the main characters. There might also be other RWBY characters who are either helping or hindering the Huntsman's journey in the Void.
Another plot idea could be a character who is mysteriously connected to the Silver Flame. They could have powers that are enhanced by it and have to hide this fact from others for some reason, like fear of being experimented on. For example, a new student at Beacon Academy discovers this connection and has to navigate through the challenges while keeping it a secret.
One common theme might be power and transformation. The silver flame across the body could symbolize a new power or a transformation that the character is undergoing. Another theme could be struggle, like the character trying to control or come to terms with this new silver - flamed aspect of themselves.
Ruby's naivete and love for all things new would have her quickly getting into the fanfic, not really caring about small flaws as long as the Guitar Huntsman concept is cool. Weiss's pride in her own knowledge of the RWBY world would make her a tough critic at first. But as she delves deeper, if the fanfic shows a good understanding of the world too, she'll start to enjoy it. Blake's empathetic side would allow her to connect with the characters in the fanfic, especially if the Guitar Huntsman has some sort of internal struggle. Yang's confidence and love for action would make her look forward to any battles or high - energy scenes in the fanfic, and she'll be disappointed if there aren't enough of them.
Well, I haven't read that exact 'rwby silver flame across his body fanfic' in particular. But generally, to find good ones, you can also check out some RWBY fan communities on Reddit or other forums. There, fans might share and recommend fanfics with such elements. Another option is to follow some RWBY fanfic writers on social media platforms as they may post about their works or recommend others.
It could be a powerful and mysterious figure from the shadows. Maybe a rogue huntsman gone bad who has his own agenda against the lone huntsman. This antagonist might have a vendetta for some past event.
It could be a powerful Grimm that has a special connection to the character in the trailer. Maybe this Grimm has been hunting them for a long time and is finally about to catch up.
Well, Ruby would likely be all eyes and ears, loving the creativity. If the Guitar Huntsman has some cool moves or a great backstory, she'd be hooked. Weiss would probably comment on the grammar and plot structure, but if it's well - written, she might start to enjoy it too. Blake would compare it to other fanfics she's read, looking for what makes this one special. Yang would be laughing and shouting at the exciting parts, like when the Guitar Huntsman battles some Grimm. Overall, their reactions would depend on how well the fanfic is written and how engaging the 'Guitar Huntsman' idea is.