The standard Wound Track of a Human in Bushido has 6 Wounds. This makes you need at least a Success level of 3 to kill a model in one hit. It’s not usual, because it’s not a game about killing. Some weaker models may have 5 wounds or less. Knowing what Success Level cannot kill a model is important to consider if an enemy attack can be lethal.
In this game, being wounded hasn’t big consequences beyond your morale, is important to know that a model with 1 wound remaining creates the same potential Threat for the enemy as a model with full health. The model probably will die in the future but, until then, he can attack, tire enemy models, use Ki feats or capture objectives at full capacity. Always bear that in mind.
This is more noticeable in Oni, Buto and other models with a large wound track + Toughness. It may seem that receiving a 5 or 6 wounds blow crippled down your poor Oni and now you are fucked. Nevertheless, that Oni still has more survivability that any average human! And it’s still a huge threat for your enemy!
It’s also important to acknowledge that those resilient models can hardly ever be killed in one hit in this game (except for Critical Strike or an amazingly high success level Combo). The attacking player would need a success level 10 and an over average damage roll, or a success level 8 and a maximum damage roll to kill an Oni in one hit. Well played this will never ever happen. So your Oni/Buto with full health is safe, good to know.
Remember, not dead = full threat.