It is incredible this was knocked out in around 72 hours or so. The level of visual polish is off the charts. Going for the pixelated look was a great decision, as it lends a unique design language in terms of the Jam entries. The programming is also pretty ambitious; the custom UI really brings a lot to the table presentation-wise. You definitely got the most out of Ren'py for this.
The story premise is cute, but I did think it was a little opaque as to what you had to do to progress. The game does have seven (!!!) endings, so I assume you're meant to play through multiple times for the optimal experience, but I felt a little lost whenever I had to make a choice to go somewhere (i.e.: will this be the choice that ends my day? It's hard to know til it happens!)
Overall, this is an excellent entry with crisp graphics, ambitious ideas and delightful writing. I had some minor gripes with how the game was paced and how events could unfurl in Yuuka's free time, but that does not distract from the experience at all. Great job!