The main antagonist could be an ancient and evil entity that has been controlling the criminal underworld from the shadows for a long time. It senses Harry's arrival in this new world (the John Wick world) and believes that his magic could either destroy it or be used to break free from its current limitations. So, it uses all its minions and resources to hunt down Harry, with John Wick standing as the last line of defense against this powerful and mysterious foe.
Another possibility is a corrupt figure within the assassin organization itself. This person could be trying to cover up some dark secrets and the ballerina is getting too close to uncovering them. So, they use their power and influence within the organization to try and eliminate her. This would add an element of internal conflict to the story as the ballerina has to not only fight an external enemy but also deal with the betrayal from within her own ranks.
Well, one possibility could be that Harry, perhaps from the Harry Potter universe, gets thrust into the dangerous world of John Wick. He could use his magic in unexpected ways in the assassin - filled world. For example, he might use a spell to disarm his opponents instead of using guns like John Wick. He could also use his broomstick for quick getaways in the city streets, adding a unique twist to the high - octane chases that are typical in the John Wick movies.
There might be a character who is secretly from the wizarding world but has turned to the dark side. This character could be after Harry in the Ouran setting, trying to use the chaos of the new environment to their advantage to get to Harry without being noticed by the Hogwarts professors.
It could be a new dark wizard that we haven't seen in the original series. This wizard might be jealous of Harry's fame and power and wants to eliminate him by making him disappear.
A jealous classmate could be the main antagonist. This person might be envious of Harry's popularity or the strange things that seem to always work out for him. They could start spreading rumors or trying to trip him up in his studies.
They could start off with some misunderstandings. Izuku might accidentally get in John Wick's way, thinking he's helping. But as they get to know each other better, Izuku would start to learn from John Wick. John Wick could see Izuku as a young, eager protege of sorts and start to teach him things like how to handle different weapons and how to read his opponents better in a fight. They would gradually build a relationship based on mutual respect for each other's skills and values.
In fanfiction, their interaction could be complex. Harry Potter is used to a world with rules and a certain way of doing things. John Wick comes from a more lawless world where he makes his own rules. At first, they might clash because of these differences. But as they face a common enemy, they would start to understand each other better. Harry might be in awe of John's determination and ability to survive in a tough world, while John would come to appreciate the power and wonder of magic in Harry's world.
Well, Harry would probably be an even more badass wizard. John Wick is known for his combat skills and survival instincts. He'd likely train Harry in self - defense from a very young age, so Harry might be more physically capable in the wizarding world. Maybe he'd use some of John Wick's moves in duels at Hogwarts.
It could be a new dark wizard who has some personal vendetta against Harry. Maybe this wizard has a grudge because Harry defeated Voldemort and he wants to prove he's more powerful, which enrages Harry and causes him to go on a rampage.
It could be a new dark wizard who has the power to manipulate minds. This wizard might target Harry specifically, driving him insane as part of a larger plan to take over the wizarding world. Since Harry is seen as a hero, if he goes insane, it would create chaos and make it easier for the antagonist to achieve his goals.