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.
It could be an orphaned wizard child from a family that was killed by Death Eaters. This would give Snape an added sense of responsibility as he might feel guilty for being associated with the Death Eaters in the past.
In such a fanfiction, perhaps the plot could involve Harry seeing a child in a difficult situation, like an orphan in the wizarding world who has no family due to a dark wizard's attack. Harry, having been an orphan himself, feels a strong connection and decides to adopt the child. He then teaches the child about magic, love, and how to face the challenges in the wizarding world.
The child could be an orphan from a small, destroyed village that Naruto comes across during one of his missions. This child might have lost their family to a powerful enemy and Naruto feels a sense of responsibility to take them in.
In this fanfiction concept, Ash's adoption could be a very heartwarming story. Maybe he meets an orphaned child during his travels. Ash, with his kind heart, decides to take the child under his wing. It could be a chance for him to pass on his knowledge of Pokemon and values like friendship and perseverance.
One idea could be that Percy discovers a demigod child who has been abandoned in the mortal world. He decides to adopt the child to protect them from monsters and to give them a proper home at Camp Half - Blood. He then has to teach the child about their demigod heritage and how to use their powers.
Perhaps the child is the offspring of a Titan. This would make for an interesting story as Percy would have to deal with the potential danger and mistrust from other demigods. But Percy, being Percy, would see the good in the child and adopt them regardless. The child might have unique powers that set them apart from other demigods, like the ability to control time or space.
The plot might be that Sakura has always wanted a family but couldn't have one in the normal way. One day, she comes across a child who has been abandoned. She instantly feels a connection and decides to adopt. Along the way, they bond over shared interests. For example, if Sakura likes gardening, she teaches the child about plants and they grow a beautiful garden together, strengthening their relationship.
Edward could be an ordinary man living in a small town. He has always wanted a family of his own but couldn't find the right partner. So, he decides to adopt a child to start his own family unit.
Perhaps Edward is a wealthy man in the fanfiction. He adopts a child from a difficult background. He uses his resources to give the child a good education, a loving home, and along the way, they both learn from each other. The child might teach Edward about innocence and new perspectives, while Edward provides stability and care.