Good concept. While well done, I feel there is a some potential wasted with it (well, its a game jam project after all, but I guess criticism is welcome). E.g the narration between levels: While I like this style in principle, it seems to undermine the value of the mechanic as storytelling device, without really adding anything.
To get a bit more precise: You have three things the player must learn to finish the game. First, that the white character acts as solid ground for the black one. Second, that the character position is frozen, while you control the other one. Third, that you can only proceed by jumping the white character into the abyss multiple times.
This would be the perfect metaphor for overcoming grief over loosing a loved one to depression. The dead remains with you and provides grounding (1), you can maybe understand him, but you cannot control his fate (2) and through his descent you are reminded you yourself must not succumb (3). This might not have been intended, but it is as it is.
The environment shows, that everyone has a different perspective (different geometry), and that the death is due to a medical condition (assets).
The narration tells, that life gets harder as we grow up (supported by the level design, good!) and that if you talk to the dead, you will recieve an answer. In my opinion the last part is a mistake. If the narration was only the living asking questions to the dead, followed up by the level that tells the answer, that would be a powerful message. The dead dont answer. This is hard to grasp, if you have lost someone. If you now can learn, that there might be an answer implicit in the way you were shaped/helped/influenced by him... bam! Alsothe first levels seemed to be at a time, where both have still been living (undermining the mechanics) furthe.
It also seemed to me, that you tried really hard to end on a high note with the ending lines, but at this point it is just stating the obvious and really got on my nerves. It felt a bit condescending, in the way kids shows are, that end by stating the moral of the episode.
This was quite harsh from my side. There is a lot to like in your game, but pointing out flaws was always more helpful to my designs than praise. So here you have it.
The narrative tools are cool, but slightly incongruent. Very frustrating, because it is so-fkn-close to being a great concept. Overall, a talented work.