It's about loneliness, how people hurt others and be hurt by others, and how everyone is just trying to become stronger in their own way. I think this songs meaning is just really deep and the message should be able to reach to anyone. The part where it says "kokoro no naka de dake hanaseru hito no kazu wa fueteiku dakara, tsuyoku naritakatta tada" which means "because the number of people whom I can speak with only inside my heart increased, I just wanted to get stronger," is specially meaning a lot to me personally.