He is neat
While acting polite in front of "friends" and strangers, he is actually sadistic and fickle, able to harm or kill another human being just to test out his abilities. His hatred of gods leads him to treat them as playthings--uncaring about what they may feel. This was shown by his physical and psychological abuse of Yato, and his replies to Bishamonten about everything that he was responsible for (Kugaha's betrayal, Ebisu's death, Tsuguha's transformation into a Karma Ayakashi).
While his hatred is mainly towards the Gods, he also seems to see humans as puppets and pathetic as well, showing disdain for them and enjoys playing with them. He often uses his brushes to control people, once causing an old woman to jump out a window while smiling and another time sending a person to be killed in a car accident and enjoying it, showing extremely sadistic, sociopathic tendencies. He can also be very petty, such as when he reveals to Yato that he kissed Hiyori for seemingly no reason other than to be a troll.
Fujisaki had been to and returned from Yomi, taking with him the first Phantom Brush (Koto no Ha). He seems to be connected to a woman with freckles, as Izanami uses this woman's looks during his time in Yomi. However, at some point in time, the woman died and this appears to have become his primary reason for loathing gods and, therefore, the wish that created Yato. This seems to be further proven by the fact that in chapter 61, Nana shows sympathy for Fujisaki, saying he must have had someone he loved who was killed by the heavens because he wouldn't have called them lowly Gods otherwise.
Fujisaki is referred to as Yato's "father". Yato was created by a wish from Fujisaki as a god of calamity. They have a master-servant relationship but they do not care for each other, though it is seen that, as a child, Yato was very happy whenever he praised him. Fujisaki has not communicated with Yato since he was forced to return to their place, meaning he does not know that it is Fujisaki whom their father is possessing at the moment. Which is why, despite having met Fujisaki before, he does not recognize him as anyone other than Hiyori's schoolmate.
In chapter 44, Father reveals himself to Yato as Fujisaki, and also tells Yato that he has kissed Hiyori.
As "Father"'s shinki, her name is Mizuchi (meaning “cruel”). She only listens to Fujisaki's orders. He also refers to her as his "kid".
Hiyori is Fujisaki's schoolmate. While walking to school one day, Hiyori accidentally steps on a soda can and trips, but is caught and helped by Fujisaki. Later, Hiyori is invited by one of her friends, Yama, to go on a group date to Capypa Land with three other guys, Fujisaki included. At the end of their date, when the parade begins, Fujisaki ends up stealing Hiyori's first kiss. Ever since then she has started avoiding him, and thus increased Fujisaki's interest towards her. In chapter 48, Fujisaki reveals to Hiyori that he is in fact Yato's dad. He continues by threatening her to stay away from Yato, to which Hiyori counters by saying that she will take him on. While being unwavering in front of Fujisaki, Hiyori later breaks down. She turns into a half-Phantom.
Izanami once mentioned in chapter 33 that Father went to the underworld to retrieve one of her brushes and Izanami, who appears to whoever looks at her as the woman closest to them, appeared as a freckled woman to Father. Since Nora is the only female Father is shown close to in the present, it could be this woman is related to him in the past and may be the reason behind his hatred for the Heavens, God, and all of humanity.
- While there are few decipherable ranges for his age, it is likely that he was alive during the Emishi War (773-811)