It's okay not to be special!

Kageyama Shigeo is called "Mob" by his peers because his bland face and personality makes him blend in with the crowd (bless that Japanese lack of understanding of English), and his subdued demeanor is what most people see when they first meet him. Shigeo is an emotional kid just like any other teenager, but because he makes a regular habit of tempering his emotions down, he rarely raises his voice or gets angry, and has a hard time getting along with people and understanding their interests or following the crowd's mood. He has a habit of not being in on the joke, young and socially unaware in general, and being socially outcast by his awkward behavior only exacerbates the situation. After several negative experiences, including a time when he seriously hurt some older kids, the reason he has a hard time expressing himself is because he is subconsciously very wary of his own powers and what he might do if he truly cuts loose. Even more than that, when most kids responded to his powers with wariness or disinterest, he found even less of a use for expressing them in front of people. Even without consciously thinking it, Shigeo has a hard time having a strong emotional reaction to stimuli, simply out of the complex he's built to protect himself and others.

Despite that, Shigeo is a very sweet and compassionate young man who hates hurting other people, and yearns for friendship and even some popularity. He never holds bitter resentment towards other people for the way they mistreat him, instead often internalizing it or even simply becoming resolved to try and improve himself to suit them. He wants to help people, and he hates the idea of using his powers on other people, but he will do whatever it takes to keep his friends and family safe in an emergency. There are many situations where responsibility for the safety of strangers falls on his shoulders, which is more than most 14-year-olds can bear and often strains Shigeo to the limits of what he can emotionally endure. Nonetheless, he can and has taken those responsibilities on himself in order to do the right thing, and when facing powerful opponents, he always tries to talk them down or to disable them rather than ever doing them serious harm.

Shigeo has always wanted to do something productive with himself, though it has taken him a long time to really understand that what he wants is to be able to do what he wants without using his psychic powers, per se. He hasn't solidly decided on what he wants to do, and he doesn't exactly hate his powers... he has joined the Body Improvement club to make up for the physical weakness he had developed from being too dependent on his psychic powers, and he has been working with his 'mentor' Reigen to seek guidance in the world. He's an impressionable kid, and consistently needs direction, which is the core of his character - he's fourteen years old, a dangerously powerful psychic, and he has literally no idea what he wants out of his life.