Hirohito was emperor during ww2, but he did not commit seppuku. There was a general, Korechika Anami, and an admiral, Takijiro Onishi, who did when Japan surrendered. Possibly others, but i'm not sure..
What does this have to do with the White racial subforum? Your question would be suited to the general or the Asian subforum. Not this one. Thanks, if you decide to post appropriately in the future.