I learned about the history of the japanese word 主人公 shujinko from Yurie Kumakura, a researcher of workers cooperatives in Japan. Goshu Nakanishi, one of the founders of the workers cooperative movement in Japan, used shujinko as an equivalent for protagonismo (which he may have learned from Jose Maria Arizmendiarrietta). The word is common in Zen Buddhism, where it is often translated as "Master," and the story goes that the Chinese monk Zuigan used to talk to himself while meditating, addressing himself, "Hey! Shujinko! Are you sleeping?" or "Hey! Shujinko! Don't let yourself be deceived by others!"
Protagonism, in the sense in which Arizmendiarrieta used it, refers to the capacity for self-activity and self-realization that each person develops as part of a collective process of self-organization. It is radically individual, something appertaining to persons, and for that reason always already collective, since the person is produced and reproduced in society. Unlike the common use of the term -- leading character -- protagonism here is something everyone develops and cultivates. An important element is the recognition of oneself as a protagonist, a kind of me<->me, an interpellation (to use Althusser's term).
Participants spend one minute walking randomly aroung the room talking to themselves out loud, like Zuigan. "Hey! Shujinko!" they call out, and then ask a question or make a comment. They then reply honestly to the question or comment. Repeat, starting each time with "Hey! Shujinko!" The questions and comments should call the person to themselves. The person calling on you is just you, not a judge, not your parent, not society, so they are challenging you to recognize things about you that you already recognize. (The zen element?)
The joker keeps time and, when time is up, may ask people to talk or write briefly about what they saw or heard and what they think about it. What did you notice when you spoke to yourself in the game? Do you often talk to yourself? When? Why? When you do, how would you describe the characters of the two selves in the conversation?
This works best as a game, as play. It is not therapy or discipline.