One way to integrate it could be through time - travel. Suppose a wizard from the future where Gundam technology exists travels back to the Harry Potter era and brings with him the blueprints for the Black Magic Gundam. This causes a stir as different factions in the wizarding world either want to use it for their own gain or fear its power and want to prevent it from being built.
The Black Magic Gundam could be a protector. Maybe it was created by an ancient wizard to safeguard the wizarding world from a great threat that was foreseen. In the fanfiction, it could be reactivated to fight against a new dark force that the normal spells and magic of the wizards can't handle.
His magic could be integrated by using spells for combat. For example, 'Stupefy' could be used to incapacitate enemies quietly. And for reconnaissance, he could use 'Alohomora' to unlock doors and access areas without being detected.
His magic could be used for stealth. For instance, the invisibility cloak could be a great asset for MI6 agents on secret missions. They could move around unseen by the enemy.
The magic in 'Harry Potter' could be used to deal with the werewolf problem in 'The Howling'. For instance, spells like the Patronus Charm could be used to fend off werewolves when they are in their dangerous state.
The black mage could be an ancient being that was sealed away long ago and is now awakened. In the fanfiction, this mage could have been part of a group that was at war with the founders of Hogwarts. Now that they're free, they seek to destroy the school and all it stands for. The story could focus on how Harry and the others discover the secrets of the founders to find a way to re - seal the black mage.
The magic system can be integrated by having spells affect the Quantum Leap process. For example, a spell like 'Apparition' could be used to quickly move between different leaps or locations within a leap. Portkeys could also serve as a means to initiate a leap or to travel to a specific time - related destination during a leap.
The magic in Harry Potter could be combined with an anime's power system by having spells work in a similar way to anime abilities. For example, in an attack - based anime, spells like the Reducto curse could be as powerful as a character's special attack. Wizards could also have to train like anime characters to master their magic, making it more of a physical and mental effort, similar to how anime heroes train to get stronger.
The magic of Aphrodite could interact with the protective spells in Hogwarts. Maybe her love - based magic could make the protective spells stronger by creating a positive emotional bond between the castle and its inhabitants. On the other hand, if her magic goes out of control, it could weaken the spells as the strong emotions she brings might disrupt the delicate balance of the existing magic.
The magic system in Harry Potter could be integrated by having characters from Highschool DxD learn spells. For example, Issei could learn the Wingardium Leviosa spell to lift objects during battle, giving him an unexpected advantage. The Portkey concept could also be used to transport characters between the two worlds quickly.
In an 'Harry Potter anime crossover slash fanfiction', the magic system could be integrated by having it interact with the anime's power system. Let's say in a crossover with One Piece. The Devil Fruits' powers could somehow interact with the magic in Harry Potter. Maybe a character with a Logia - type Devil Fruit could turn into a magical element like fire, which could then be used in combination with a fire - based spell from Harry Potter. This would create new and exciting magical abilities that are a blend of both universes.