I love how you used the gameplay segments to illustrate Marisa's aging. It made me sad to witness have powers decline. Mortality is a terrible thing. It was super effective.
On that note, it was a bit disappointing to not have dialog options to turn Marisa immortal. I know it would have missed the point of the game, but the options I had went completely against how I felt. Although I've only gotten ending C, so I may be missing something. Maybe Enoko decided to save her from her foolishness in the other routes? I hope so, and I may be replaying the game to find out.
The gameplay is both really cool (3D shmup where you can shoot in all directions and the default orientation changes along the course? I've never seen that, and that's interesting!) and kind of meh. I tried to go for a no-miss run to get another ending, but a bullet sniped me and I didn't feel motivated to try again since there is a lot of downtime. Having the dialog be unskippable is not great for alternative endings.
Echoing some of the other comments, the hitboxes felt big enough that the best option was to macrododge most of the time. There were a few points (I think the 2nd last wave of stage 3?) where you kind of get trapped if you don't know the enemies are about to fire a huge wall at you.
To summarize, I think the game succeeds in conveying what was intended, and the gimmicks employed were effective. It just needed a bit more polish.