An Interactive Experience
Mirror is an interactive narrative about the struggle of balancing social life and private life. While encountering NPCs stands for meeting new people, breaking through blocks of obstacles represents overcoming personal challenges.
The two separate tasks affect each other since the two avatar moves in sync. For example, dashing through obstacles might makes your social figure bumps into other people, just like we sometimes focus too much on our personal affair and become offensive unawarely. On The other hand, neglecting personal challenges might leave your internal ego too far behind, which leads to self-destruction (game over.)
Besides desynchronization, moving backwards too much or losing all hearts also leads to the bad ending. The former is a metaphor of indulgences in the past, and the latter means a total mental breakdown.
Whenever you meet a new NPC, they are going to give you a first impression, which is "like" (you gain a heart), "dislike" (you lose a heart), or "neutral" (nothing happens.) After you receive their first impression, you can choose either giving out a heart or do nothing. If you give out a heart, you take the risk of receiving negative feedback from the NPC you react to, even though they might liked you in the first place, but they might also give you hearts in return to your sincerity.
Whenever your internal ego leaves too far behind, you have use your hearts to rejuvenate, which will cost one heart, but will bring forward your internal ego without moving your social figure. You can also reach out for angels, representing outside help to gain extra heart.