I really like the direction and portrayal of Shiori’s love. A large theme has been transient mortal existence; Hinako’s life is only a brief period compared to Shiori’s immortality. It’s only natural that a monster will view love to be all-consuming because humans are so vulnerable.
Not only is Hinako targeted by other monsters (which Shiori takes responsibility for), Hinako is constantly contemplating suicide. Even if she manages to live until old age, what’s a hundred years compared to thousands? Shiori wants Hinako to only look at her due to a mixture of guilt, selflessness, and selfishness.
Hinako showed Shiori that there was a life outside of just being a monster; Shiori is not condemned to permanent loneliness and fear simply because of her birth. To repay this kindness, Shiori wants to overwrite Hinako’s sadness even if it’s distorted by a monster’s sense of possessiveness. This is the only way that Shiori understands love and can love, since she never had a family herself.
It’s also noted that Shiori never really does anything monster-like. She’s like one big dog that follows Hinako around. She doesn’t go around eating or terrorizing people because she’s too busy trying to flash a bright neon sign to Hinako’s ultra dense black hole denial.
Edit:
Taking a second read: Shiori and Miko keeps noting Hinako’s smile. It’s not coincidental that after Shiori’s conversation about wishing her happiness, Hinako begins to smile more often. A shallow read would be to assume that Hinako is simply becoming happier, but it seems more like she’s trying to show that she’s happier. This goes back to if Hinako really understands Shiori’s desires. It’s cute (Hinako is a little emotionally unaware) because Hinako is really trying even if she doesn’t quite understand it.