Fujimura Group

Fuji-nee's family home.
Illya is freeloading off of them during the epilogue of the Saber route.
Fuji-nee's grandfather, Raiga, is their boss, and her father (who was adopted into the family as a son-in-law) is a reliable, taciturn giant of a man.
Perhaps it was these people and their anything-goes attitude that caused Fuji-nee to turn out the way she did?
Shirou often helps out Old Man Raiga with his hobbies, and gets a fair amount of spending money in return.

Fate/side material: Fate Encyclopedia
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fujimura-group