Sinon from Ggo could also be very interesting. If she were to enter Sao, her sniper skills might translate in unexpected ways. She could be paired with characters from Sao and learn new combat techniques while also teaching them about the precision of long - range attacks.
Ruby. She has that innocent and curious nature which would make her reactions in the SAO world really interesting. She could be fascinated by the virtual world and its different rules, and her positive attitude might be a source of hope for the other characters. Also, her scythe - using skills could be adapted in the SAO combat scenarios in unique ways.
I think Naruto and Kirito would be an interesting pair. Naruto is all about his exuberant and determined personality, always believing in his strength and the power of friendship. Kirito, on the other hand, is more of a lone wolf type at first but also has a strong sense of justice. Their meeting could lead to some great character development for both. Naruto could teach Kirito about the value of relying on others more, and Kirito could show Naruto some advanced combat strategies that he has learned in SAO.
One idea could be that the main characters from Sao end up in Ggo due to a strange glitch in the virtual world systems. They have to adapt to Ggo's different rules and combat styles while also trying to find a way back to their own world in Sao.
Raphael could be really interesting. In the 2003 version, he is hot - tempered and tough. In the 2012 version, he also has a strong personality. Seeing how he reacts to his counterpart and how they might either clash or bond could be a great focus. Maybe they have a friendly rivalry as they compare their fighting skills.
Ross could be really interesting. Since he's an archaeologist, in a crossover with a show like 'Indiana Jones' (in a fanfiction sense), he could go on an adventure with Indiana Jones. Ross would bring his academic knowledge while Indy would have the practical experience. Their interactions would be filled with Ross trying to over - analyze everything and Indy just wanting to get the job done.
Chiaki Nanami could be an excellent choice. She is the Ultimate Gamer, so if you cross her with a digital or virtual world, there are so many possibilities. She could use her gaming skills to navigate through a new digital realm, like a Matrix - like world. Her calm and intelligent nature would also make her a great character to lead the group in a crossover situation. She could figure out the rules of the new world quickly and help the others adapt.
I think a pairing between Klein and Togusa could be fascinating. Klein's more laid - back nature compared to Togusa's by - the - book style could lead to some interesting interactions. And they could both bring different skills from their respective worlds when facing challenges in a crossover situation.
Definitely Damon Salvatore. He's the bad - boy vampire with a heart of gold (sometimes). In a crossover, he'd be a wild card. He has his own sense of justice and loyalty, but also a devil - may - care attitude. He could get into all sorts of trouble in the world of the Originals. His sarcastic remarks and his ability to charm his way out of (or into) situations would make for some great scenes. He might also form an unlikely friendship or rivalry with one of the Originals, like Kol perhaps. His backstory and his experiences in 'The Vampire Diaries' would contrast and collide in interesting ways with the Originals' world.
Naruto himself would be very interesting. His energetic and determined personality would make for great adventures in the GTA world. He would probably approach the chaos and crime of GTA with his usual enthusiasm, trying to bring justice in his own ninja - way. His ability to make friends easily could also lead to some interesting alliances with GTA characters.
Ruby would be really interesting. Her energetic and optimistic nature would contrast greatly with the often dark and power - hungry characters in the Overlord world. She could inspire some of the downtrodden minions with her belief in the good of people. Also, her scythe skills and speed would be a unique addition to the battles in the Overlord universe.