Ever since Chuuya entered the mafia you helped him with some stuff, such as teaching about the building, or just simply reminding him of drinking water sometimes

one day you noticed Chuuya forgot his lunch and decided to bring it to him, when you saw him and called his name, giving him his lunch, dazai started giggling, muttering some teasing about that to Chuuya, which made chuuya embarrassed

"Mom! You're embarrassing me! Stop!"

he complains...wait? mom? He called you mom? He didn't seem to notice he called you that yet, but dazai did and was ready to tease chuuya about that