Ghosts like that seem to have somewhat symbiotic relationships with high energy people. As shown, it's only sampling her energy, and it's also killing and eating all the other ghosts that show up. While still an evil ghost, it's not the worst kind.
that big ghost is so jerkass. using Hana's spirit power like a stove lolz although this here explain why Hana keep getting hungry. it is because her spirit power getting sapped out by those ghosts, not because she is a huge eater. at least I'm glad that Miko isn't there to go inside that abandoned building. since Miko can see those ghosts, I'm worried she would be passed out seeing so many ghosts inside