Going off on a limb here, and theorize that before he died, Miko's father was the same as Hana, in that he had extremely potent aura just like her. And when he died he pretty much became an "alpha" spirit. What I mean by that is that other, weaker spirits automatically submit to him and obey his orders. Also because his family made a shrine for him, they accidentally managed to crate something of a holy place in their house, even further increasing her dad's power. This might be why spirits flock to Hana so much, because she too has the potential to become an "alpha". Weaker spirits are drawn to stronger ones, even if they're still alive.