Harry Potter could be one of the main characters. He might be the one who discovers Draco in this strange situation and has to decide whether to help him or leave him be, given their past rivalry.
One possible plot could be that Draco is in a situation where he is being controlled by a leash for some magical or political reason. Maybe he's being paraded as a symbol of a new order in the wizarding world. His former Slytherin pride is put to the test as he has to endure this public display.
One character could be Viktor Krum. Since he is from Durmstrang, he might play a role in Draco's new life there. Maybe he becomes a mentor to Draco or a rival in some magical competitions at the school.
A female wolf might also be a main character. She could be attracted to Draco's unique submissive nature, which is different from the more dominant male wolves in the pack. Their relationship could develop in an interesting way, with her helping Draco gain confidence while he in turn shows her a different way of looking at the pack's social structure.
One possible fanfiction could be about Draco using a harness leash in a magical creature training scenario. Maybe he's trying to tame a rare and unruly beast, and the harness leash is a special magical tool. He has to use his Slytherin cunning to figure out how to work with the creature while using the leash effectively.
In 'leash on draco fanfiction', it could center around a power dynamic. Draco is often seen as a proud and somewhat haughty character. So having him on a leash could represent a shift in power. For example, another character might be in charge of him, and this could lead to all sorts of interesting interactions, like the character using the leash as a means to make Draco do things he wouldn't normally do, or it could be a part of a redemption arc where Draco has to submit to certain conditions to grow as a person in the fanfiction world.
One possible fanfiction could be about a magical creature Draco that is tamed and put on a leash by a powerful wizard. The wizard might be using Draco for some sort of mission, like exploring a dangerous enchanted forest. Draco could be a dragon - like creature with its own will, and throughout the story, it struggles against the leash both physically and emotionally as it tries to assert its independence.
Draco and a harness leash could be part of a story where he's in a magical circus. He's in charge of some magical animals and the harness leash is what keeps them in line. But Draco might start to have second thoughts about keeping these animals in captivity, and the harness leash becomes a symbol of his internal struggle between duty and compassion.
Ron Weasley often makes an appearance. He might be suspicious of Draco's intentions towards Hermione and try to protect her. His loyalty to Hermione and his hot - tempered nature can add a lot of drama to the story.
Narcissa Malfoy could also be important. As Draco's mother, she might have mixed feelings about the situation. On one hand, she wants to protect her son, but on the other, she might see the potential good in Harry and Draco working together for the baby's sake.
Hermione could be one of the characters. She might initially be skeptical about Draco's situation but then be moved to help him out of a sense of justice or because she realizes the implications of a pregnant wizard being caged. Another character could be Harry Potter. He could be conflicted about helping Draco given their past history, but still feel compelled to do the right thing.