Art's brother's death + Ratio speculation
Art's brother died in a bus accident related to the terrorist attacks on Minimum Holders. But who had been with him...?
Can you imagine if Ratio had been there, along with the rest of the group? And maybe Art's brother didn't die immediately, maybe he lived long enough so that Art and Nice could find him and tell him that it'd be okay and they'd get him to a hospital--
-- and then Ratio takes one look at Art's brother with his Minimum and breaks down into tears because he knows it's too late.
Everyone brought something to Art's brother's grave except for Murasaki and Ratio. Even Birthday brought something. Obviously Murasaki didn't know him, but... What if Ratio had been so traumatized by the accident that he just wanted to keep it pushed out of his mind? What if Birthday knows this, which is why he brought such a large quantity of treats to the grave, to make up for Ratio's absence?
What if this is why Ratio reacted so strongly when they found Chiyuu in the alleyway? Or when that kid was injured in episode 8, who he stopped to help?
Him and Birthday are so reliant on each other, it's not even funny. If something were to happen to one of them, both of them would be in trouble. Any arguments they have must be pretty scary.