How to write the characters

[brythain]

Just a couple of small points:

1) If you have somebody real in mind, that can be helpful—especially if you're close enough to them to see between the lines, in a manner of speaking.
2) If you have a clear theme song for a character, playing it repeatedly while writing may help you get into the spirit of things.

[Guest Poster]

Oh, a better example may be her "experiments", but fanon is blending with canon there.

(I know I've at least read fanfic that's implied that she will intentionally do a "bad" experiment just to troll Lilly.)

Yeah, fanon is probably blending with canon there. In the VN, Hanako's convinced that Lilly's eventually going to walk out on her the moment she gets bored or displeased with her and it seems she's already afraid to make waves with Lilly (by bringing up her misgivings about Lilly's mothering of her) for exactly that reason. Her deliberately trolling or pranking Lilly would imply a confidence in the stability of their friendship that Hanako doesn't display in the VN.

[Zykes]

Just a couple of small points:

2) If you have a clear theme song for a character, playing it repeatedly while writing may help you get into the spirit of things.

In my case, I feel this is quite true, though I think this method really boils down to how one's "Creative juices" actually work.