He is Sawamura Minori's manager at BNB toy company.
None. Apparently, he and Emiri Yuu knew each other for a while, but there's no love interest between them.
Fukusei is created by Chihiro Harumi, and he has no information regarding any inspiration used to create him. Fukusei first appears in chapter 4 of Koi o Suru no ga Shigoto Desu volume 1. (In chapter 8, his name is revealed.)
His usual attire is not what a normal white collar man wears. He wears casual clothing to work.
He is very supportive of Minori.