"Having him be masked, but also fractured, is a very intentional thing,β says Abrams (via Reddit). He continued, "like that classic Japanese process of taking ceramics and repairing them, and how the breaks in a way define the beauty of the piece as much as the original itself.β"
Abrams is talking about the Japanese art of Kintsugi, also known as Kintsukuroi. This is the concept of repairing broken pottery and gluing the pieces back together. The point is to treat this brokenness as something that is not to be ashamed of. Abrams connects this saying, βas fracted as Ren is, the mask becomes a visual representation of that. There's something about this that tells his history. His mask doesn't ultimately hide him and his behavior is revealed."