If this were a proper Seppuku ritual then she would have a Tanto; the short blade or dagger before her, an assistant (Spike I guess?) would use the Katana or long sword to decapitate the Alicorn Princess. Actually the female practice of suicide, known as Jigai just had them using a knife to cut their throat. But with her magic I guess she could do it by herself using the Katana. You go girl.