There could be original characters created by the fanfiction author. Maybe a lone hero or a group of rebels who have a unique ability or knowledge that gives them a chance to stand up to Sauron. They could add a fresh perspective and new storylines to the 'Sauron Gets the Ring' concept.
Some fanfictions might include characters like Gandalf trying to oppose Sauron even after he has the ring. Gandalf could be devising new strategies or trying to find a way to counter the overwhelming power that Sauron now wields. Aragorn could also be a character, still trying to unite the people against Sauron's tyranny.
One interesting plot could be Sauron using the ring to reshape Middle - earth in his own image. He might start by corrupting all the remaining free lands and turning them into dark, desolate places filled with his minions.
It's likely that there is a female protagonist who is on a quest related to the ring. She might be strong - willed and intelligent. And then there could be a male character who is initially her rival but later becomes her ally in the journey involving the ring. There might also be a sidekick character, like a small magical creature that helps them along the way.
Obviously Naruto would be one of the main characters. There might also be his friends like Sasuke and Sakura. But since it's a fanfiction involving a special millennium ring, there could be new characters created specifically for this story who are also important.
There's no way to be certain without reading it, but perhaps there's a female lead who is somehow connected to the ring. Maybe she has a special ability that is awakened by the ring, and there could be a male character who helps her on her journey with the ring. There could also be an antagonist who wants to steal the ring for their own malicious purposes.
Obviously, Lucy is one of the main characters since the fanfiction is centered around her getting burned. There might also be characters like her family members, such as her parents or siblings, who could play important roles in her recovery process.
Well, Hermione is obviously a main character since it's about her getting even. Harry and Ron might also be involved as her friends, either helping her or being caught in the middle of her revenge plot.
Percy is surely a main character in this fanfiction. Depending on the universe it's set in, if it's related to a series like Percy Jackson, characters such as Annabeth, Grover, or his other demigod friends might also be important characters. They could either be the cause of Percy's anger or the ones who try to calm him down and help him through his angry state.
Obviously, Ginny is one of the main characters. Since the title is about her getting 'the talk'.
Another character could be Astrid. In the fanfiction, she might play a role in Hiccup's journey to get stronger. She could be his training partner or offer advice based on her own skills and experiences. Also, there might be new characters introduced, like an old dragon trainer who has a lot of wisdom to share with Hiccup.
Steven would be the main character as he's the one getting poofed. But depending on the context, the Crystal Gems - Garnet, Amethyst, and Pearl - would likely be important characters too. They would probably be involved in the aftermath of Steven getting poofed, either trying to revive him or dealing with the situation his poofing has caused.