Well, Sonic is the main character in most Sonic the Hedgehog time travel fanfictions. He's the face of the franchise and his adventures through time are what drive the story. Knuckles is popular as he has a connection to the past through his role as the guardian of the Master Emerald. His knowledge of ancient things can be very useful when Sonic travels back in time. Rouge is also a character that features often. Her thieving skills and her ability to gather information can be handy in different time - based scenarios. And then there's Metal Sonic. He can be an interesting addition as he might be sent through time by Dr. Eggman to cause trouble for Sonic, or he could be a part of some time - warped experiment gone wrong.
Jaina Proudmoore is often featured. She has a lot of emotional depth and her actions have had a great impact on the story. In time travel fanfiction, she might go back to when she was younger and make different choices regarding her relationships and her role in the war. Arthas Menethil is also a popular character. His fall from grace is a well - known and tragic story. Time travel could be used to explore if he could have been saved from his dark path, perhaps by going back to his early days and changing certain events or influences.
Boruto himself is obviously a very popular character to feature. Since it's a Boruto time travel fanfiction, he's usually the main focus. Naruto is also popular. When Boruto travels back in time, his interactions with his father Naruto at a younger age are often explored. Sasuke is another one. His skills and knowledge can be important in helping Boruto in the past, or Boruto might discover something new about Sasuke's past during his time travels.
Amuro Ray is a very popular choice. He's such an iconic Gundam character. His skills as a pilot and his complex personality make him a great fit for time - travel adventures. He could use his knowledge from different timelines to change the fate of the Gundam universe. Another one is Char Aznable. His charisma and his long - standing rivalry with Amuro can add a lot of drama to a time - travel story.
In sonic the hedgehog crossover fanfiction, Sonic himself is of course the main character. But other characters that are popular to include are Amy Rose. Her love for Sonic can create interesting relationship dynamics in crossovers. Another popular one is Dr. Eggman. His villainous nature can be a great source of conflict in crossovers with other characters. And then there are characters from other video game series that are also quite popular, like Link from The Legend of Zelda. His use of weapons and exploration skills could make for some really exciting crossovers with Sonic.
Jon Snow is very much a favorite in asoiaf time travel fanfiction. Given his complex backstory and his role in the fight against the Others, fans often write about him traveling back in time to change certain events. Arya Stark is also popular. Her skills as an assassin could be put to different uses in different time periods. For example, she could go back in time to protect her family members from harm.
The Lone Wanderer is quite popular. Their heroic deeds in the main Fallout games make them a prime candidate for time - traveling adventures. Also, Courier Six. Their mysterious background and skills could be explored in time - travel scenarios.
Jotaro Kujo is quite popular. His strong and stoic personality makes for interesting interactions in different time periods. Dio Brando is also a common choice. His villainous nature and powerful Stand, The World, can create a lot of chaos when time - travel is involved. And then there's Jonathan Joestar. His noble character can be a great contrast to the more modern and complex characters when he's brought into different timelines through time travel.
Ryoma Echizen is often a popular choice. He's the main character in the original series, so it's natural that many time travel fanfictions would focus on him. Fans like to explore different scenarios with him, like how he would react if he met his past or future self, or how he would use his skills in different time periods.
Zero Kiryu himself is often a central character. Since it's his name in the title, fans love to write about his adventures through time. He can be portrayed as a hero trying to fix things in the past or future. Another popular character is his closest ally. In many fanfictions, this ally might accompany him on his time - traveling journeys and provide support or different perspectives. And often, the main antagonist from the original story also makes an appearance. Writers like to explore how the antagonist would react to time - traveling events and how Zero Kiryu would deal with them in different time periods.
Mario and Sonic are at the top of the list for sure. But in addition to Luigi and Tails, Princess Peach is often included. She can bring an element of needing to be rescued or she could also be a strong character helping out. Knuckles from Sonic's world is also popular. He has his strength and knowledge of the Chaos Emeralds, which can be crucial in a crossover story. There are also some fans who like to include Bowser and Dr. Eggman as the main antagonists, which makes for an exciting story.