Well, clearly Harry Potter and Sirius Black are the main characters. Harry is the protagonist of the original series, and here he has a special connection with Sirius as he rides him. Sirius, in his animagus form of a large black dog, provides the means of transportation and is also a very important character in the Harry Potter universe.
One possible story could be that Harry discovers a new magical ability while riding Sirius in his animagus form. This ability allows them to communicate telepathically and they go on an adventure to find a hidden magical artifact.
Obviously, Harry Potter and Sirius Black are the main characters. Harry is the young wizard who has lost his parents and now is adopted by Sirius. Sirius, on the other hand, is Harry's godfather who takes on the role of his adoptive father. There may also be other characters like Hermione and Ron who could still be Harry's friends and play important roles in the story, providing support and getting involved in their adventures.
Obviously, Harry and Sirius are the main characters. Harry, the protagonist of the Harry Potter series, and Sirius, his godfather.
Neville Longbottom could also play a more prominent role. Neville has his own growth arc in the series, and after Sirius's death, he could bond more with Harry over their shared experiences of loss. They could support each other in their fight against the Dark Arts. And perhaps some of the Death Eaters who were involved in Sirius's death could be main characters from the antagonist side, as Harry tries to track them down and bring them to justice.
The man could be an Animagus who has the form of a large, rideable creature. Harry might not know at first and then discovers the truth during the ride.
'Him' could be a centaur. In the Harry Potter universe, centaurs are intelligent and powerful beings. Harry might ride a centaur in a situation where he needs to quickly cross the forest and the centaur's speed and knowledge of the terrain would be very useful.
Definitely Sirius Black. Fanfiction writers can really dig into his backstory, from his time at Hogwarts as a Marauder to his unjust imprisonment in Azkaban. His rebellious spirit and his love for Harry are often portrayed in great detail. Harry Potter is also a great character in these fan works. His journey of self - discovery while having Sirius as a sort of surrogate father figure is really interesting to read about. And then there's Dumbledore. In some fanfictions, Dumbledore's actions and motives regarding Sirius and Harry are explored more deeply, adding new layers to his character.
The main characters are Harry and Sirius. Harry is the famous wizard boy from the Harry Potter series, and Sirius is his godfather. In this fanfiction, they are likely to be at the center of the story, with their relationship and the events related to the 'happiness hamper' being the main focus.
The main characters are Naruto and Sasuke, obviously. They are two of the most iconic characters from the Naruto series. Naruto is known for his exuberant and determined personality, while Sasuke is more brooding and focused on his own goals, and in this fanfiction, their relationship in the context of Naruto 'riding' Sasuke is what the story likely revolves around.
Obviously, Hermione is one of the main characters. And the werewolf that she rides is also a main character. There might also be other characters from the original Harry Potter universe that play supporting roles, like Harry or Ron who could be involved in the story in some way, either helping Hermione or being against her actions regarding the werewolf.