My thoughts on how I would've written it:
This. Well, sans the stupid expression in the painting of course. Having her be surprised to be painting him since he's on her mind a lot would be a fantastic moment.
Hanako: I can think of two great options for her, actually.
1) Tearfully ranting about how she doesn't think anyone could ever love her, letting slip accidentally that she loves Hisao, after which he holds her or kisses her or whathaveyou.
2) Her showing character growth and nervously (and quietly) telling Hisao that she does.
Shizune: Hisao tries to sign it to her, but he's not good enough at it yet and she gets gradually more confused and aggrivated until he just grabs her hand and places it over his heart.
Lilly: This one seems like it would be the most calm and natural of them all. It would just slip out.
Emi: Perhaps Hisao would have another medical scare while training with Emi and as she's freaking out over being so stupid as to push him too hard, he calms her down in the Nurse's office by telling her how he feels.
Those are all kinda cheesy I know, but then again, most real life confessions are if you think about it.
"There are worlds out there where the sky is burning, and the sea's asleep, and the rivers dream; people made of smoke and cities made of song. Somewhere there's danger, somewhere there's injustice, somewhere else the tea's getting cold. Come on, Ace. We've got work to do." - The Doctor, Doctor Who