Funny, I never thought about it being handwritten, but it looks like it at a second glance, when you mention it
. But at a third glance...
I wonder who wrote it, I'm pretty sure it wasn't Ayu herself. I'm also quite sure that it's been either edited in Illustrator, or any other vector supporting application, or done in there from the start. Some lines is too perfect... it actually looks very vectored, so now I don't think it's handwritten anymore, haha.