He wore the mask because people thought he was a monster and he had no real way of proving otherwise.
Now, he has a letter of introduction from a renowned merchant and a pretty boy next to him that can validate that he's indeed human.
For anyone who care, personally I find the backstory of that bully a little tragic.
tl;dr is awkward kid tried to talk to his childhood crush, but others mistook his intention (other kids, the girl, makoto...well, makoto is more of "I don't know or care") to be bullying the girl who's a noble that 'abandoned her people to run away'
After this he keep trying to contact her, hoping to sort things out, but since Makoto order his people to prevent him from getting close to her the kid could never do so and the misunderstanding never solved.
He eventually get manipulated by the demons and turned into a monster and get killed.
Though a glimpse into an alternate reality where Makoto never come to this town show that he will get turned anyway since the demon plans doesn't involve Makoto but eventually regain his sense and join Hibiki...only to get microwave'd by that timeline's crazed Makoto....'egg in a microwave'....
@Mizumachi its slowly revealed that Makoto have huge apathy in persons life, the only exception are what he considered close friends and thats why when he lose those on other timelines, killing is just a job to get what he wants.
Ilumgand is really just awkward and unlucky. Unlucky enough to meet powerful factions that frankly don't give a shit about him. Don't forget that Makoto is twisted in the head, and almost nobody in Asora has goodwill towards humans unless they're family or a source of benefit. Makoto isn't a 'good' MC, but a selfish one.
I forget, why's he going to an academy in this city at all in the first place? I know the merchant's daughter/s told him to get Makoto to enroll there, but what's Makoto's actual goal in attending? Does he just wanna learn more "normal" magic?