The Headmaster didn't die and made it to the agency building. No one even about atsushi past or what the headmaster did to atsushi but dazai, ranpo and yosano has suspicions on a few things.

atsushi didn't know why the headmaster was there, the headmaster was talking about something but atsushi didn't pay any attention

Kunikida: "atsushi?"

atsushi was shaking, dazai just smirk, he knew atsushi was about to snap

Kyouka: "atsushi..are you okay?"