Think about his skills and abilities. Maybe he has an uncanny ability to communicate with magical creatures that most others don't. This could lead to him befriending a dangerous creature that the other students are afraid of. His skills could also put him in the spotlight, either for good or bad. If he uses his skills to help solve a problem at Hogwarts, he could become a hero. But if he uses them in a way that goes against the school's wishes, he could be in trouble. All of these aspects would help develop the character of Corvinus in your Harry Potter fanfiction.
You can start by giving him a unique backstory. Maybe he grew up in a wizarding family with a dark secret that he's trying to uncover. This would give him a sense of purpose.
Give him some distinct personality traits. For instance, he could be extremely curious but also a bit of a loner. This would make his interactions with other characters more interesting. He might be the type to explore the Forbidden Forest alone just to satisfy his curiosity. And when he does interact with others, his loner nature could lead to some awkward but also endearing moments. He could also have a strong moral compass that sometimes conflicts with the rules of Hogwarts, making for some great internal and external conflicts in the story.
Chapter 665, "Give You a Good Lesson on Behalf of Your Mother!", is the clearest early answer because it turns Behalf's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Why should I get so many points?
Chapter 859, "I Bet She Won't Last Ten Minutes!", is the clearest early answer because it turns Shuiyun Mountain's situation into a concrete plot event. It opens with All morning, the two little ones were quiet, not making a peep, even...
Chapter 631, "It's Him Who Got Hurt, Then It's Fine", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 20. Early on, Several people turned their heads upon hearing the sound and saw three...; later, the chapter leans on She was clad in a long black dress, and the dull color did not hide her....
Chapter 711, "It's Actually Her", is the clearest early answer because it turns Zhang Jing's situation into a concrete plot event. The chapter turns that into something concrete by moving from Zhang Jing immediately became wary and hastily signaled the several...
Chapter 698, "Brother Yan Was Just Forced!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Li immediately asked for some tools and colored paints.
A practical answer is Chapter 3, because it turns the idea into a concrete scene. The chapter opens with Qiao was still annoyed at the attitude of this unknown girl when she heard..., adds pressure through So without a second thought, she blurted out a fierce challenge, "Fine, if..., and ends on.
Chapter 12 is the strongest chapter-level answer because it starts from Qin?" Jiang Li called out twice, and only then did Mrs. and follows through on The glass shattered on the floor with a crash, attracting the attention of....
Chapter 505, ""Postpartum Care for Sows", is the clearest early answer because it turns Shang Shaobai's situation into a concrete plot event.
Chapter 852, "Could That Be an Aphrodisiac Spell?", is the clearest early answer because it turns Rong Junsheng's situation into a concrete plot event. It opens with Rong Junsheng's words startled Shi Lei and Rong Kexi.