In his human form, Acnologia might be more complex. As a dragon, he's mainly seen as a destructive force. But as a human, he could have emotions like regret, love, or compassion. For example, he might feel remorse for the destruction he caused as a dragon.
Acnologia in human form would likely have a different sense of morality. As a dragon, his actions were mainly about survival and dominance. In human form, he could be influenced by human values. He might start to care about things like justice and equality. He could also be more vulnerable in human form, both physically and emotionally, which would shape his personality in a way that is very different from his all - powerful dragon self.
He might have a tall and imposing stature, with piercing eyes that still hold a hint of his otherworldly power. His hair could be a dark color, perhaps black or a deep shade of purple, and it would be neatly styled.
A really interesting plot could be Acnologia in human form forming an unlikely alliance with the Fairy Tail guild. He could be on a quest to redeem himself for his past dragon - related atrocities and the guild helps him in some way. This could lead to many adventures where he has to use his human skills and not just his dragon powers.
His loyalty would still be a big part of his personality, but it could be expressed differently. Instead of just following Natsu around like he did as an Exceed, he might try to support Natsu in more strategic ways as a human, using his newfound human intelligence.
He might become more empathetic in his human form. Since humans have a wide range of emotions and experiences, Kurama could pick up on these and become more in tune with the feelings of others compared to when he was just a fox demon.
His strength could show up as superhuman physical abilities. He might be able to lift extremely heavy objects with ease.
One idea could be that in their human forms, Happy and Carla are part of a detective agency in Magnolia. Happy is the enthusiastic junior detective while Carla is the more serious and observant one. They solve mysteries related to magic items that have gone missing, often running into other Fairy Tail members who unknowingly hold clues.
His dragon form could be a large, black - scaled dragon with red eyes. The scales might be shiny and have a sort of metallic sheen to them. He could have huge wings that span a great distance when fully extended.
Well, in many Fairy Tail Natsu Dragon Form fanfics, we often see an expansion of Natsu's powers. Some fanfics might explore his new abilities in more detail, like how he can control different types of dragon magic that he couldn't in the original series. It's really exciting to read about his enhanced combat skills and the unique ways he uses his dragon form.
He might become more empathetic. As a dragon, he was all about power and domination. But as a human, he could start to feel the pain and joy of others, which would soften his once - harsh personality.
Natsu is very impulsive. This might make him overprotective of his daughter in the fanfiction. He might jump into action at the slightest sign of danger to her. For example, if she's in a simple sparring match in the guild, he might be tempted to interfere if he thinks she's in real danger.