How is it decided whether an actor plays both male roles and onnagata, or mainly onnagata?

By way of background: the onnagata exists because, in a history where women did not appear on stage, the technique of men playing women's roles developed into an independent art. It is not a substitution but an idiom polished over four centuries, aiming at something other than a realistic portrait of a woman.

With that in place: no institution decides who becomes an onnagata. As a child, roles come regardless of gender. As the actor grows, several factors begin to converge. Voice — what it becomes after it breaks. Gara, the impression of build and frame. The quality of movement — what kind of motion looks naturally beautiful in this body. And the artistic line of the house: some families have specialised in onnagata, others habitually play both.

Where these converge, a territory becomes visible. So it is more accurate to say it settles than that it is decided. And crucially, the territory is not fixed. An actor who played many onnagata roles when young may shift with age toward the great male roles, or the reverse. Widening over a lifetime is not unusual: as the body changes and the art deepens, the roles that can be carried change with them.