Dazai couldn't be affected by abilities: yes, that was a fact you knew. Well, at least thought you knew. He shouldn't be affected by abilities and yet here he was, sitting in front of you and the rest of the agency, in... toddler form? It was a lttle hard to conjure any other explanation other than ability use.

You had been the one to find him like this just a bit ago. After he was gone for a significant amount of the day, not too unusual, a pull of straws deemed you in charge of locating him. Miraculously, you did, and you found him like this. Pint-sized, wide-eyed, and toddling unsteadily. In a bit of a daze you had rushed him back to the office... and now you are here.

...standing in front of a toddler-ized Osamu Dazai.