Sirius, being a brave and resourceful wizard, could form an alliance with other powerful wizards and witches who oppose Voldemort. Together, they could create a shield around Harry. He could also use his animagus form to spy on Voldemort's followers and gather intelligence to prevent any attacks on Harry.
Sirius could use his knowledge of the wizarding world's secrets. He might know some hidden places or spells that could keep Voldemort at bay. For example, he could put a powerful protective charm on the place where Harry is staying.
Well, at first, Sirius would be in a state of shock and panic. But then he'd have to step up. Their relationship would shift from one of equals (in a sense, as Harry was growing up) to a caretaker - cared - for dynamic. Sirius would have to learn about Harry's likes and dislikes as a baby. He'd sing lullabies to him, comfort him when he cries. This new experience would make their bond stronger in a very different way. Harry might not remember all of it when he's turned back, but there would be a subconscious change in how he feels towards Sirius, a deeper sense of security and love that stems from those baby - days when Sirius was his whole world.
Their relationship would be severely damaged. Harry would likely feel betrayed by Sirius. After all, Sirius is supposed to be one of his protectors. It would be a huge breach of trust. Sirius, on the other hand, would probably be filled with guilt if he realizes his mistake. He would have to work hard to regain Harry's trust, if that's even possible in the context of the fanfic.
Sirius would probably be very protective. He'd use his magic to create a safe and comfortable environment for Harry. For example, he might conjure up soft, warm bedding for the baby. He'd also try to find the best baby - wizarding supplies, like magic - infused milk bottles that ensure Harry gets all the nutrition he needs.
Sirius influences Harry's early life by being a protector. He stands as a shield against any potential threats. He might use his Patronus, a large dog, to guard Harry at night, making Harry feel safe in his sleep.
Some might write it to explore a different side of the characters. It's a way to show how Harry and Sirius could be pushed to their limits and what they would do in extreme situations.
Sirius would probably be overjoyed at first. Harry is his godson and he cares deeply for him.
Sirius would probably be very worried and immediately try to help Harry. He might use some basic healing spells he knows.
Well, their relationship would be in tatters. Harry would probably avoid Sirius like the plague after such an event. Sirius, on the other hand, would be at a loss for how to deal with what has happened. He might feel betrayed, even though he knows Harry was forced. This would create a huge rift between them that would take a lot of time and effort, if ever, to mend. It would also change the way they interact with other characters in the fanfiction, as their relationship was an important part of the overall story dynamic.
Sirius would have a big impact on Harry's understanding of family. Harry has always longed for a real family, and Sirius would show him what a loving and supportive family can be like. This would make Harry more open - hearted and less guarded. He would also be more likely to forgive those who have wronged him in the past, as Sirius might teach him the value of forgiveness. Moreover, Sirius' love for adventure could make Harry more adventurous in his exploration of magic and the wizarding world.
In a 'Harry and Sirius join Voldemort' fanfiction, it might start with Voldemort making a very tempting offer. For Harry, it could be something related to saving his friends or family. Sirius might be lured by the idea of protecting Harry in a different way. However, once they join, they would face a moral dilemma. They would have to pretend to be on Voldemort's side while still holding onto their own values. And there would be a lot of internal conflict as they see the evil deeds happening around them.