What is wrong with this story?

It is risible

It is total and complete rot. You could stand on a flyover with pen and paper and jot down the license plates of passing vehicles and string them together and it would read like Shakespeare compared to this bunk. Absolutely godawful.

It gives the reader no reason to engage with any aspect of the "plot", the IQ of the reader is lowered also no twist can redeem it, EVERYTHING is wrong with that story as it now has the obvious title of Grim, Just Plain Grim.

I get ya head

Well first of all.
In the description of the story. The first sentence is incredibly long. Why did you say 'he never expected'. You would be better off saying. Need to work on the description as it is the first thing readers see.
As for the story, well you are telling everything, instead of showing. Your not describing anything, like the cake. Or the calendar. The character doesn't have any thoughts or opinions, so he's not relate able. You need to say what he is thinking. The opening chapter, is about him about to cut a slice of cake, not interesting at all. I know its his birthday, but why is he doing it alone. Why did he buy himself a cake, you need to say why. Everything you write needs to have a reason behind it, if it doesn't get rid of it or give it one. The first chapter is really short and choppy, The dialogue is very childish. And just goes back and forth. Another thing you are doing, is you keep continuing the story through the chapters,You need to end the chapters and then start fresh on the next, dont have him still be in the same situation each time. Another thing, your characters seem to perfect. Oh look at me I have superpowers Im great I can shoot needles out of my hands. You need to make your characters flawed, relate able. The plot is going no where and is very boring and cliche. A boy with powers or Zodiac powers or what ever it is, is being hunted, he joins with a group of people just like him. Its been done a million and one times. You never described anything, what the people look like, the robots, why is was like when Grimm used his scorpio thing. The whole thing is just choppy and childish.