The portraits could offer him emotional support. Just seeing his parents' faces might give Harry the strength to face difficulties. For example, when he's feeling down or facing a tough decision, looking at the portraits could be like getting a warm hug from his parents, even if they're not physically there.
The portraits can act as a source of emotional support. Just seeing their faces and the expressions of love and pride on them can boost Harry's confidence. For example, when he's feeling down about his latest encounter with Voldemort, a glance at their portraits might give him the strength to keep going.
One interesting story could be that the portraits of Harry's parents start to interact with other portraits in Hogwarts in a very unusual way. They might form a sort of 'portrait alliance' to protect Harry even from within the frames. For example, they could pass on secret messages to Dumbledore's portrait which then gets relayed to the living world.
He would probably be overjoyed. Harry has always longed for a connection with his parents. Getting their portraits would be like getting a part of them back. He might just stand there, staring at the portraits with a big smile on his face, unable to take his eyes off them.
Sirius Black's portrait is often popular. Fans like to imagine how his portrait would interact with the other portraits in Grimmauld Place. He was such a dynamic character in life, and his portrait could continue to be a rebel within the frame, perhaps causing chaos among the more proper portraits.
Another concept is that the portraits have emotions and desires that are more complex than what is shown in the original books. They might long to be free from their frames, or they could form relationships with the living characters. Some portraits could even fall in love with a wizard or witch passing by, leading to all sorts of interesting and sometimes comical situations.
Discovering the family portraits could make Harry feel less alone. He has always felt like an outsider, but seeing his family members in the portraits, hearing their voices and stories, could give him a feeling of being part of something bigger. He might start to think of himself as not just Harry Potter, the boy who lived, but also as a member of a large and important wizarding family with a rich history.
In this fanfic, perhaps Harry stumbles upon the portraits while exploring a hidden part of Hogwarts. He might have an emotional moment as he sees his parents for the first time in this way, and the portraits could start interacting with him, sharing long - lost memories and advice.
One unique idea is when the portraits of Harry's ancestors can come to life and physically interact with the present world. For example, they might help Harry in a battle against dark wizards by using ancient spells they knew. It adds an exciting dimension to the story.