I let this game consume pretty much all of my non-work hours today, and that could be the whole comment, but it'd be less than this deserves so I'll add some more.
This is the type of narrative that could only exist as a visual novel, and there's something, I think a really good mix between the tools of the medium that you use to great effect and the tools of narrative that you forego not because they don't suit what you wanted to make, but because you knew you could do without and deliver the intended experience even better that way. It's a case of knowing the box so well that you can craft a narrative outside of it no problem. It's great.
The use of the heatwave as a concept very similar to the horrible euphoria of some of the scenes with Angel is clear and striking with no need for over-explaining, and the presentation, sound design and visual design work extremely well together.
This is the type of game I browse itch.io and participate in game jams to eventually find. Heatwave will stay with me inside my mind for a while, and I'll take my time chewing on it.