Hajime Hinata is also a great option. He has a relatable and determined personality. In a crossover, say with a detective - themed world like Sherlock Holmes' London, he could use his deductive skills (which he developed during the events of Danganronpa 2) to solve new mysteries. His journey of self - discovery in Danganronpa 2 could also be further explored in a different setting, as he tries to find his place in the new crossover world.
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.
Makoto Naegi from Danganronpa and Yu Narukami from Persona. Makoto's determination and leadership skills could pair well with Yu's calm and collected nature. They could work together to solve the mysteries that occur when their worlds collide.
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.
A really interesting pairing could be Makoto Naegi and Natsu Dragneel. Makoto, with his positive and determined attitude, could befriend Natsu easily. Natsu's impulsiveness and Makoto's more level - headed thinking could create an interesting dynamic. They could team up to face challenges, with Makoto providing the strategic thinking and Natsu the brute force.
I think Makoto Naegi and Robin would make an interesting pair. Makoto represents hope and Robin is always there to support Batman. They could learn from each other's positive outlooks. Also, Kyoko Kirigiri and Batman himself could be a great pairing. Kyoko's detective skills are top - notch, and she could either assist Batman or be a bit of a mystery for him to figure out as she has her own secrets.
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.
Frisk could be a very interesting character to focus on. Frisk has the power of determination, which could be used in unique ways in the FNAF setting. They could befriend some of the animatronics, using their kindness and determination. Also, since Frisk is the player - controlled character in Undertale, it would be interesting to see how they adapt to the more dangerous and unpredictable world of FNAF.
Kuroko himself would be very interesting. His unique 'phantom' style of playing basketball could create some really unexpected scenarios in a crossover. For example, if he were in a crossover with a detective story, his ability to be unnoticed could be used to solve mysteries in a very unorthodox way while still having some basketball - themed elements in the story.