Cool powers and lore can be interesting, and it is important to flesh out your world to make it feel more robust, but if that's all you got, I'd much rather just read a wiki article that summarizes your concept than have to slog through a whole book where the main character is mainly a display piece for how cool the powers are, and a tour guide to show off you world. I think what your friend is trying to get at is that he wants to see how the powers psychologically effect and change Tanuc himself. What emotions and struggles and drives and social connections does Tanuc have to get us invested in him as a person?
It sounds like you already have the seeds for several key conflicts with Tanuc that you can explore. Consider the following character developments:
1) His father figure, the one who created him, is a monster of his own making, a body-warped cannibal who must commit terrible deeds to maintain himself. Is Tanuc horrified of this? Does he not care? Does he sympathize with his father, or think him a fool who deserves his fate for going too far? Does he perhaps admire his father for trying to transcend his limits?
How do these reactions define Tanuc's outlook on life? Will he attempt to follow his father's footsteps or reject him? In either case, how does this emotional impact cause him to react when he discovers similar situations on his adventures? (Does he have a disdain for scientists because of his discomfort with his father, or does he admire them as he admires his father?)
2) Tanuc does not know he is an animal turned human. Yet, how does the fact that he is an animal effect his psyche and ability to relate to people? Does he perhaps get along better or feel more comfortable with animals, or at least other racoons/tanuki? Do other humans make him uncomfortable or skittish? Does he not like even being touched by humans because of this? Does he ever wonder WHY he has these feelings, and does this wondering bring him closer to the revelation of his true nature? Does he maybe have a disdain for animals that a racoon would naturally fear or prey upon?
Alternately, does he like being human, and would the revelation that he is an animal send him into an existential crisis? Does he have a human love interest whom he fears losing if his true nature is revealed? Is he uncomfortable around animals due to some subconscious feelings that conflicts with his human wants?
3) Tanuc has no memories of his time before awakening as a human. Does this bother him in any way? Is he haunted by the lack of memory, of wondering who he was? Does he wonder about his parents (if he knows his father isn't his biological father)? Not knowing he is an animal, does he fantasize about an idealic childhood in a human village that he believes he has forgotten?
Or does he not care about the past, and thinks mainly about the future? Perhaps a core belief of his is that one's origins do not define a person, its their actions. That could even be a theme of the book, if he encounters people from different walks of life who have a lot of baggage, and maybe he can be the one who shows them that the past doesn't have to be a shackle. And if this is his belief, does the revelation of his origins shake this belief, or does it strengthen it?
4) What does Tanuc think about the Chimera Bracer? Does he realize how special he is? If so, does this make him worry about potential dangers associated? Or does it go to his head, leading to an overall prideful attitude?
These are all possible avenues of character development just going off what you've given us, but the thing is, you haven't even described his baseline personality enough for me to even guess what Tanuc's reaction to such things would be. That's what I think your friend is trying to suggest, that beyond the powers, you should focus on how those powers, and his life circumstances, affect him.