It was one time. Years ago. He met a woman for a brief moment, and it ended in a one night stand. She was beautiful and intelligent, and her mysterious aura could have lured in any man. Young Fukuzawa didn't think much of it. It was 16 years ago, after all. Right after, the women basically disappeared. It was almost like she never existed. Nothing could be found on her. Turns out she didn't even have an ID

So explain why Atsushi walked into his office, with a 16 year old following him with traditional clothing and...fox ears...-?

Turns out the woman was a kitsune

Atsushi- "Um- this kid is claiming to be your child-?"

Somewhere in the office it sounded like Dazai said something about a scandle with the president, and then a thwap, probably Kunikida shutting him up