To be fair, I think it’s more about the porn but I’ll watch in interest with you.

Haibara Hikimori wears a mask primarily as a visual representation of his lifestyle and self-perception.

The character is a social recluse, who has withdrawn from society to live in isolation. The mask serves several functions within his character design:

Social Detachment: It physically manifests his desire to hide his face from the world and avoid direct human connection. So when others move in it’s his way of hiding in plan sight.
Self-Image: Hikimori is depicted as having low self-esteem regarding his physical appearance—described in character profiles as being overweight and “ugly”, and the mask allows him to interact or observe others without exposing his real face.