Seppuku, or as most in the West call it hara-kiri, is ritual suicide by cutting open the abdomen. It originated with the samurai class and was considered an honorable way to die. Over time it would even become a standard judicial punishment for samurai, if they hadn’t done so already before their arrest.
It was intended that you would perform this act along with a second, or kaishaku, who was expected to cut off your head with a single stroke of their sword immediately after your cut. This would shorten the time of suffering and was not considered murder. The kaishaku was carefully chosen from your samurai companions to be a skilled swordsman. But not all who committed seppuku had a kaishaku and you can imagine how awful their deaths were as a result.
But over time seppuku fell out of favor in Japan (although suicide for honor reasons did not) and when it happens now, it’s considered an anomaly and out of place in a modern society. How did that change happen? It’s of course complicated but highly related to the Meiji restoration and the opening of Japan to the West in the 19th century.
Interestingly, the Japanese art of drawing the sword, iaido, has a kata where the practitioner acts as the kaishaku for a samurai committing seppuku. There were some astonished looks in the class when our sensei explained the basis of that kata.