The confessional is a mechanic in Persona 5.
The confessional can be found in Kanda Church. The protagonist will be able to bring a party member with him, and by having them confess their guilts in the private booth, they'll be given the ability and option to relearn one old skill. By doing so, time will pass.
All of a character's Personas share the same list of skills, so it doesn't matter how different evolutions interact with one another within the system. The only exception is the special skill given to second-tier Personas when the Confidant of their user is maxed out. The same applies for their third-tier Personas in Persona 5 Royal.
The protagonist is unable to bring Morgana to the confessional with Mercurius, as that Persona is only able to be used on December 24, a day when the protagonist can't partake in daily activities. In Persona 5 Royal, the next time Morgana is able to participate in battle is on January 9, but the confessional can only be used after his Persona has evolved into Diego. The same applies for Goro Akechi and Sumire Yoshizawa with their third-tier Personas, Hereward and Ella respectively, as their awakenings only occur after the calling card for Maruki's Palace is sent.
- If Morgana is brought to the confessional, the protagonist will come inside to translate for him.