Hardest? Slogging through the middle. I can pretty much envision the beginning and the end, but the middle is like pulling teeth. Well, it's that and editing. There is a sort of thrill associated with editing, but it's also hard work.
Easiest? Coming up with ideas. Like germs, they're everywhere.
Most fun? When the going is good, it's very, very good.
Most tedious? Finding names and coming up with other superficial qualities for characters. These things, I don't care so much as the personality--which I always think up first.
Coolest? I'm going to borrow the other person's answer in that I get to make stuff up!
Least cool? Sending stuff out. Waiting. Receiving rejection letters.
Best? Finally finishing something.
Worst? Just finding the time to write. (You might argue: Well, find the time to write, you lazy bum! I try. I really, really try.)
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I'm getting some recent inspiration from Mushishi, a fantasy/supernatural/horror anime. For anyone who likes subtle and creepy, give this a go.