Dazai would be the epitome of the Fun Parent™. 
He would take his kid to amusement parks, funhouses, swimming, basically any and everything for chuuya raising a kid in the mafia, surrounded by death, blood, and misery. But he tries his hardest to keep his child away and untouched by the darkness. 
He has told very few, trusted people about his kid, because he’s afraid enemy organizations might target his family.
He’s very smug when his kid shows a preference towards him instead of their mother.