Viability: There is a defined beginning and end, and I like having the option to restart to try something different. I agree with the comment talking about how having the affection show up as a number sort of taking me out of the immersion, so written descriptions of the griffin's reactions to your actions would be cool, so you have a feeling on whether or not you're doing well, without having to be explicitly told.
Presentation: I'm not sure if having the action options pop up after the main text does any favors? I think it's fine to have all the text show up together. Overall I think having more dialogue would be beneficial, for the sake of overall storytelling and immersion, and also for us to get to know the griffin we're making friends with.
Theme: is very clear! I think the color palette for the most part works well, I personally would change the border color from a gray (which is a very similar value to the teal) to something else (maybe a much darker version of that teal, just as an example, any significant change in value, lighter or darker, I think would look better). Also changing the color of the hover text would be good to do too! I also think it'd be good to add more dialogue elaborating on the griffin altogether, how it looks, the actions it performs, how it's feeling, etc., so we feel a more personal/realistic connection to the creature we are supposed to want to help. But overall I think the theme is very sweet :)
Engagement: I think having more options, and more text (exposition, more vivid descriptions of the environment and situation) would help with overall attention-keeping and replayability (a curiosity to *want* to get more endings).