It's possible that there's a character who is like a mentor to Harry in his tiger - fan journey. This person could have years of experience with tigers and teaches Harry about their behavior, habitat, and how to be safe around them. There may also be some other young fans like Harry who he meets and they form a group to promote tiger awareness.
Since I haven't read it, I can't say for sure. But it could be the tiger itself as a main character in a sense. Maybe there's a zookeeper or a hunter who also plays a significant role.
Bella is the central character as she is the 'daughter' in the title. The tiger is also a main character. There could be a wise old owl or a friendly deer that act as side characters, guiding Bella or helping her in her journey related to the tiger.
The main characters are clearly ryguyrocky and Tina the tiger.
There could be a doll collector named Alice. She might be Harry's friend or rival, always competing to get the best dolls in the story.
Hermione could be a main character. She might be the one who helps Harry understand and control his gorgon powers. For example, she could research in the library to find ancient spells or potions that can suppress the gorgon - like effects when they are unwanted.
There might also be a love interest for Harry. This character could be someone who is also involved in the dangerous world of assassination in some way. She or he might be a fellow assassin or someone who is on the periphery of that world but still gets drawn into Harry's life, adding a romantic sub - plot to the story.
There could be the mafia boss. He might be a tough and shrewd character who takes Harry under his wing at first but later becomes suspicious of Harry's actions. Another main character could be Harry's best friend in the mafia. They go through all the dangerous and exciting adventures together, and this friend might have different views on the mafia life compared to Harry.
In this fanfiction, there could be new characters introduced as well. There might be an older, wiser wolf that takes Harry under his wing, so to speak, and teaches him about the ways of the wolf. Or perhaps there's a villain who is specifically after wolf - Harry for some dark purpose.
Obviously, Harry is the main character as he is the duke. But often, there will be his loyal servants like his butler, Mr. Thompson, who helps him manage the ducal estate. And there could be a female lead, perhaps Lady Elizabeth, who is a love interest and also provides support in different situations.
There could be new characters introduced in this fanfiction. For instance, a powerful dark wizard who is an equal match for the ruthless Harry. This character could be the main antagonist, constantly challenging Harry and forcing him to use his ruthlessness to the fullest. Or perhaps a mysterious mentor figure who helps Harry hone his ruthless side, teaching him skills and knowledge that are not part of the traditional Hogwarts curriculum.