In persona one, the party called out to their Personas, in persona 4, the party called their persona via will inside the TV world
In persona 3, the party sort of....forced them out by evoking their power
In persona 5, it's the mask, and something that bothers me an the mask is that it can make established Personas take another form, essentially corrupting them. I know I might be looking into this way too hard but it bothers me.