The most important character is surely the hungry caterpillar. But we can't forget about the things it interacts with. The fruits and food items it consumes play a role too. They are like the little friends or obstacles in the caterpillar's journey. For example, the big leaf at the end where it forms its cocoon is also kind of a character in the story.
Given the title 'the hungry man story', the protagonist is the hungry man. He could be any person in a story that is dealing with hunger. He might be a beggar on the street, a man in a famine - stricken area, or someone who has lost his means of getting food. The story will probably tell us more about his character, his reasons for being hungry, and what he does to change his situation.
The central character is the hungry monster. However, there can be a whole host of other characters. There could be a group of squirrels that the monster encounters in a forest. The squirrels might be hoarding nuts and the monster has to figure out how to get some. There could also be a hermit - like old man living in a cottage who offers the monster some strange but delicious - looking food. And perhaps there are some mischievous imps that play tricks on the monster while it is searching, adding more twists and turns to the story.
Orochimaru is a very likely character. He has always been shown to be extremely power - hungry in the original Naruto series. He's constantly seeking new ways to gain more power, whether it's through experimenting on others or trying to obtain the Sharingan. Another one could be Kabuto. He was influenced by Orochimaru and also had a strong desire for power. He tried to absorb all kinds of powers and knowledge to become stronger. And Madara Uchiha is also a candidate. His plan to create the Infinite Tsukuyomi was mainly driven by his thirst for power and his desire to reshape the world according to his own will.
You could write a romantic fanfic where they have a forbidden love story. Maybe Cassandra saves the Doctor in a dangerous situation and their relationship blossoms from there.
The most important character is the hungry caterpillar. It's the one that drives the whole story forward by its actions of eating and growing. And then there are the things it consumes, such as apples, pears, plums, etc. They are not really characters like the caterpillar, but they play a part in the caterpillar's story. So basically, it's mainly about the caterpillar and the things it interacts with in terms of food.
The primary character in the story is the little caterpillar. It's a hungry little fellow. Other elements in the story are the food items it consumes. These food items play an important role as they are what the caterpillar interacts with, but they are not characters like a living being with its own actions and motives other than being eaten by the caterpillar. So mainly, it's the little caterpillar that drives the story forward.