The Catharsis Effect is a primary element in The Caligula Effect
Named after "catharsis", or the purge of strong emotions such as fear and anger, the Catharsis Effect is a sudden outpouring of raw emotion caused by a great upheaval or an intense situation. Normally, these out of control emotions would turn a person into a Digihead, but with assistance from Aria (and their own resolve to face their pain), the output can be managed to allow the person to exhibit supernatural abilities while still maintaining their sanity. The result is that the person spawns a specific weapon and additional accessories such as masks. Catharsis Effect aesthetics are unique to each individual, but some similarities exist, such as a thorn surrounded by flowers erupting from the person's chest
In the game, the Protagonist is the first to awaken their Catharsis Effect, by confessing to Aria the pain that drove them to Mobius and releasing it in a violent burst. Everyone else gradually awakens their powers as the game progresses.
In Overdose, Aria is capable of "Catharsis Effect Overdose", which acts as a release on Aria's regulation of power output from the Catharsis Effect. This is demonstrated in the Go-Home Club's Overdose Attacks and whenever the GHC fights against Lucid and the Musicians they lead. However, Overdose is risky as it puts a strain on the users, hence why Aira limits the Overdose. If released to full effect, the users will receive an incredible power boost, but may run the risk of breaking down. Thorn herself questions whether or not they will be able to recover from it during their final confrontation.
In the anime, Shogo is the first to be shown with a Catharsis Effect, while everyone else awakens their power in episode 6. Strangely, Ritsu is capable of awakening a Catharsis Effect without Aria's assistance.