There is more honor in ritualistic self-sacrifice, than a humiliating defeat at the hands of your enemy.
The player who wins Seppuku may choose to immediately kill all their figures in the Province. If they do so, they immediately gain 1 Victory Point for each of their figures killed this way and also gain Honor for each of their figures killed this way. (Note that this may change the Honor tiebreaker for the following War Advantages.) If a player decides to perform Seppuku, they must kill all of their figures; they cannot choose to leave some in the Province. Note that the player is still in the Battle, even if they no longer have any figures in the Province.