He might use his Patronus. His Patronus could guide Harry out of a dangerous place or ward off Dementors that were about to attack Harry.
Well, perhaps Remus arrives just in time to save Harry from a group of Death Eaters. He uses his werewolf skills and magic to fend them off.
A fanfic could be centered around a magical plant that has the power to cure lycanthropy. Remus hears rumors of this plant in the Forbidden Forest. He ventures in, facing various magical creatures and dangerous terrains. When he finally finds the plant, he has to figure out how to use it properly. This could involve a series of trials and errors, and perhaps some help from Hagrid who knows the forest well.
Remus might become more submissive in a way. Since he is now Harry's familiar, he has a certain obligation to follow Harry's lead. However, he would still retain his intelligence and wisdom. For example, in a battle, he might be more likely to wait for Harry's command rather than act on his own instincts immediately.
One possible fanfic could be about Remus Lupin's search for a permanent cure to his lycanthropy. It might involve him traveling to far - off places, meeting with ancient healers or magic users who claim to have the knowledge. Maybe he teams up with some of his old Hogwarts friends like Sirius or James in flashbacks, and they try to find a cure together. This would add an element of friendship and adventure to the story.
They could start by sharing their deepest secrets. Harry could tell Remus about his nightmares and fears about Voldemort, and Remus could open up about his struggles with being a werewolf. This sharing would create a strong bond between them.
Growing up with Remus would also expose Harry to a different side of the wizarding world. Remus has connections with various magical beings and outcasts. Harry would then be more open - minded about different magical cultures and species. He would not be as quick to judge based on what he has been taught at Hogwarts, but rather form his own opinions. This would shape him into a more well - rounded and worldly wizard compared to the Harry we know from the original series.
It deviates mainly in the character identities. In the original, Harry and Hermione are just normal students with their own roles. But in this fanfiction, becoming Remus' pups gives them a completely different identity. They might have new powers or behaviors that are not in the original. For example, they could have enhanced senses as pups.
In some fanfics, Snape might help by using his knowledge of the situation. He could provide crucial information that clears Harry's name. Maybe he has some insights into Sirius' situation or the events that led to Remus blaming Harry that others don't have, and he decides to share that information to set things right.
Remus would be horrified. He'd probably quickly take the cutting tool away from Harry.
It can change the narrative by adding a new support system for Harry. Instead of just relying on his friends, he has Remus in a more intimate 'mate' role. This could lead to different plot developments, like Harry making decisions based on Remus' advice more often.