I feel like the drawing by Yuuma in that last panel is a clue.
Maybe I'm just being a schizo but I think the shadowy "bad guy" here is his biological father and the "mom" is a stepmom who came into the family some time after his real mother died. Everything that Yuuma does is basically because he misses his biological mom, and the stepmom's seemingly paranoid reaction to his antics only worsened everything. We also have only ever gotten his perception of his parents and so far have never seen their side of the story. Of course there might still be a supernatural angle to this story too, like perhaps he is doing the 100 stories thing because he's trying to summon the ghost of his mom to kill him or something. But these are all just conjecture.