Love and acceptance are huge themes too. Harry has been through so much, and in these fanfictions, the oc shows him unconditional love and acceptance. It's not just about giving him a home, but also about accepting his flaws and his destiny. The oc often has to fight against the prejudices of the wizarding world to keep Harry safe and loved, which adds an interesting layer to the story.
There's also 'The Adopted Savior'. It's a fanfiction where the oc is from a different magical world and adopts Harry Potter. It's really cool because it combines elements from different magical cultures. The oc brings in new spells and ways of thinking that change Harry's perspective.
Perhaps Bruce Banner adopts Harry Potter after the events at Hogwarts. He takes Harry to the world of science, showing him things like advanced laboratories and scientific research. Harry, in turn, shows Bruce the wonders of magic. Their bond grows as they learn from each other, and together they face new threats that combine elements of both the magical and scientific worlds.
It could be a young wizard who lost their parents during the final battle against Voldemort. Harry feels responsible for all the orphans created by the war and decides to take this particular child under his wing.
Another theme is self - discovery for Harry. With the influence of the MC, Harry gets to explore different aspects of himself. For example, he might discover new magical abilities or gain more confidence in his identity as a wizard. In some fanfictions, the MC helps Harry to look beyond what he thought was possible for himself.
Well, one possibility is that Harry realizes Fenrir's tragic backstory and decides to help him change. Maybe he uses magic to suppress Fenrir's werewolf side and tries to integrate him into the wizarding society. Harry could teach Fenrir about friendship and loyalty, and together they fight against the dark forces that once exploited Fenrir.
The girl might be a descendant of an old wizarding family that has fallen on hard times. Harry adopts her to revive the family's honor. She could have some special knowledge or heirloom that attracts Harry's attention and makes him decide to take her in.
The combination of two very different universes. Ichigo from Bleach is a very different character from those in Harry Potter. His unique powers and personality, when put in the context of the wizarding world, create a lot of interesting scenarios.
Perhaps the girl is a huge fan of Harry Potter in the fanfiction world. When Harry discovers her, she's being bullied for her love of him and his story. So, he adopts her to protect her. He then shows her the real Hogwarts, not just the one she's read about. Along the way, they might face challenges from those who don't like the idea of Harry having an adopted daughter, but they overcome them together.
Well, Elrond could use his ancient wisdom to train Harry in magic that's different from Hogwarts. Maybe he'd teach Harry about elven magic, which could give Harry an edge in fighting Voldemort. Elrond's knowledge of ancient spells and potions could be a great asset to Harry.