Okay whoever did the art AND the sound effects need a raise because what the hell seeing Mr. Hemlock's monster form actually scared the heck out of me! Especially when he smiles and you hear this creaking noise- my god I got so spooked my back hit my chair. I have to say the art is so good and the dialogue all felt natural, especially to Lucy who really shone through with her edgy and slightly rude teenager.
I have to say, I was curious what you meant by "non-romantic" yandere, I know there are platonic yanderes so I was curious how Mr. Hemlock would exhibit this but from what I can see, there's no "real" affection from him. So that made me wonder, if you take away any form of affection from a yandere, what makes it different from just a psychopath.
Then I remembered that no matter WHAT ending you get, Mr. Hemlock will continuously stalk Lucy. He's pretty much obsessed with Lucy but not in a lovey kind of way but I feel like he's ACTUALLY committed to making Lucy experience or work through her fear like some sort of twisted psychologist/teacher. So he's obsessed with Lucy in the way that a yandere will be obsess over their object of affection, but for Mr. Hemlock it isn't out of love but a desire to make Lucy face her "fears". I think he targeted Lucy because she's a prime target to hold fear: she's isolated, alone, nobody takes her seriously (as evidence to that godawful school counselor, like seriously LET THE GIRL TALK), she has a reputation of being weird and freaky, and she's a teenager who's experiencing all of these emotions in a very intense way.
Also, I looked up what Hemlock symbolized and from what I can tell, it symbolizes death, poison, betrayal, danger, toxicity, sacrifice, interconnectedness, endurance and longevity. I can honestly tell that betrayal is a very key part here, because no matter what ending you get Lucy feels betrayed that Mr. Hemlock, no matter what she does whether it's accepting, moving on, or killing him, he'll always return to haunt Lucy. Also ties in line with endurance and longevity, either from Lucy's side of enduring Mr. Hemlock's continuous dangerous presence or Mr. Hemlock for going after Lucy.
I also think he poison's Lucy's mind, especially in Ending 1. People who are driven by fear often act impulsively and uncharacteristically of themselves which happened to Lucy. She might be an edgy teenager but she wouldn't resort to killing given her environment. It was only after Mr. Hemlock came that he began to change her.
I just have to say that I love this, I love how Mr. Hemlock feels so suffocating and eerie and would love to see how Lucy can still hold on to her sanity with how her "homeroom teacher" keeps scaring the heck out of her. Amazing job to everyone that created such a cool experience!