I don’t know what Mishima’s goal was, and maybe he didn’t either, but his actions signaled his understanding of the many masks that we all wear. Suicide pulled the last mask from his face.
Whenever I get bored or frustrated, I think of Yukio Mishima because he is the example of a truly less-than-heroic person who had nothing special except for an rich mind and inner life and he was able to externalize that life in some spectacular ways, including his own death.
I have no such need to die quickly or even spectacularly but I can learn from someone who did.