One Piece Card Game · Rules Explained
K.O. vs. Trash in the One Piece TCG
Not every Character that goes to the trash was K.O.'d. In the One Piece Card Game, a K.O. means being trashed after losing a battle as the attacked Character, or being K.O.'d by an effect, and nothing else. The difference decides whether [On K.O.] effects happen and whether "cannot be K.O.'d" protects a Character.
What a K.O. is
K.O. is a keyword with a narrow definition. The rules here are from Bandai's Comprehensive Rules, version 1.2.1, last updated August 28, 2026, current as of October 2026, and Bandai's rules Q&A.
Comprehensive Rules · 10-2-1-1
"K.O." is a keyword that refers to a Character card being trashed on losing a battle, or a Character card being trashed due to a card's effect.
"Due to a card's effect" means an effect that says K.O. As an instruction, K.O. means placing a Character from the Character area into its owner's trash (rule 10-2-1-2). Rule 10-2-1-3 then closes the door on everything else: a Character trashed by some other method is not treated as K.O.'d. Only Characters can be K.O.'d. A Leader can't leave the Leader area at all (rule 3-6-3), and losing a battle it is attacked in costs it Life, not the card.
Every way a Character leaves the field
Card text groups all of these as being "removed from the field", which means moved from its area to another area (rule 4-11-2). Only the first two are K.O.s.
Whatever the route, two things always happen. Any DON!! given to the Character goes back to its owner's cost area rested (rule 6-5-5-4). And the card stops being the card it was: if it comes back into play later, it is treated as a new card with none of its old effects, its [Once Per Turn] effects can be used again, and it can't attack on the turn it is played again (rules 3-1-6, 3-7-4 and 10-2-13-4).
What "cannot be K.O.'d" protects
Rule 10-2-1-3 says "cannot be K.O.'d" and similar effects only apply when the card would be K.O.'d by an effect or a battle. Read the rest of the wording too, because most protection is narrower than "cannot be K.O.'d" on its own:
When a protected Character loses a battle it is covered against, it stays in play: an effect that prohibits an action takes precedence over one that requires it (rule 1-3-3). The attacking player still won the battle; the K.O. simply doesn't happen.
How [On K.O.] works
[On K.O.] activates when the Character with the effect is K.O.'d on the field. Its conditions are checked there, the effect is activated there, and then the card goes to the trash, where the effect resolves.
Comprehensive Rules · 10-2-17-1
[On K.O.] is a keyword indicating that when the card is K.O.'d on the field, the activation timing is fulfilled and you should check whether the activation conditions have been met. If all the conditions have been met, the effect is activated on the field. After that, the Character card with the activated [On K.O.] effect is trashed, and the [On K.O.] effect is resolved while the card is in the trash.
Three consequences come from that. A condition like "[Opponent's Turn] [On K.O.]" is checked while the card is still on the field. Any K.O. counts, whether it comes from losing a battle, your opponent's effect or your own effect. And Bandai's Q&A confirms the effect is about this Character being K.O.'d, not about it K.O.ing something else.
"Instead" effects: changing how a Character leaves
Effects with the word "instead" are replacement effects (rule 8-1-3-4). Some replace one way of leaving the field with another, and that can turn a non-K.O. into a K.O. or the other way round. The replaced part is treated as an effect of the player who owns the replacement (rule 8-1-3-4-7).
Marco
OP17-015
K.O. this Character instead of another being removed, then its [On K.O.] can replay it
LittleOars Jr.
ST30-009
Trash this Character and draw instead: a trash, so no [On K.O.]
Marco is the clearest case. Bandai's OP17 Q&A (August 21, 2026) says Marco can K.O. itself instead when it would be returned to hand or placed at the bottom of the deck by an opponent's effect, and that when Marco and another of your Characters would be K.O.'d at the same time by an opponent's effect, you can use it so only Marco is K.O.'d. Because Marco is K.O.'d by an effect, its [On K.O.] activates, and if you trash a card with a type including "Whitebeard Pirates" from your hand, Marco is played again from the trash. LittleOars Jr. replaces removal with a trash, which is not a K.O., so any [On K.O.] it had would not activate.
An example
Your Characters include Fugar, Gyukimaru and Marco
You have 5 Characters and want to play a sixth. You reveal it and trash Fugar to make room. That trash is rule processing (rule 3-7-6-1-1), so Fugar's [On K.O.] doesn't draw you a card.
On your opponent's turn, an effect tries to K.O. your active Gyukimaru. It can't be K.O.'d by your opponent's effects while it is active, so nothing happens to it.
Your opponent plays Gloriosa to place Gyukimaru (cost 4) at the bottom of your deck. That isn't a K.O., so Gyukimaru's protection doesn't apply.
With Marco in play, you can K.O. Marco instead, and Gyukimaru stays. Marco was K.O.'d by an effect, so its [On K.O.] activates, and you may trash a card whose type includes Whitebeard Pirates from your hand to play Marco again from the trash.
On your next turn Gyukimaru attacks and is rested. If your opponent then attacks it and wins the battle, it is K.O.'d: its protection covers effects only, and only while it is active.
Common mistakes
Activating [On K.O.] for the Character you trashed to make room for a sixth. That is not a K.O.
Treating "cannot be K.O.'d" as protection from bounce or bottom-of-deck effects.
Trashing a Character because its power reached 0. It stays in play.
Keeping DON!! on a Character after it leaves. The DON!! goes back to the cost area rested.
Saying a Leader was K.O.'d. Leaders take damage; only Characters are K.O.'d.
Frequently Asked Questions
What is the difference between K.O. and trash in the One Piece TCG?
A K.O. is a Character being trashed because it lost a battle or because an effect K.O.'d it (rule 10-2-1-1). Both put the card in the trash, but only a K.O. activates [On K.O.] effects and only a K.O. is stopped by "cannot be K.O.'d". A Character trashed any other way is not K.O.'d (rule 10-2-1-3).
Does trashing a Character to play a sixth one count as a K.O.?
No. It is rule processing, not a K.O., so the trashed Character's [On K.O.] doesn't activate (rule 3-7-6-1-1 and Bandai's rules Q&A).
Does "cannot be K.O.'d" stop bounce or bottom-of-deck effects?
No. It only stops K.O.s. An effect that returns the Character to its owner's hand, places it at the bottom of the deck, or makes its owner trash it still works (rule 10-2-1-3).
When does [On K.O.] activate?
When the Character with the effect is K.O.'d, by a battle or by any effect, yours or your opponent's. It doesn't activate when that Character K.O.s something else (Bandai's rules Q&A). The effect is activated on the field and resolved after the card is in the trash (rule 10-2-17-1).
Can a Leader be K.O.'d?
No. K.O. only applies to Characters (rule 10-2-1), and a Leader can't be moved out of the Leader area by effects or rules (rule 3-6-3). A Leader that is attacked and loses the battle takes damage instead.
Is a Character with 0 power K.O.'d?
No. Power can go to 0 or below and the Character stays on the field (rule 1-3-6-1-1 and Bandai's Q&A). It is only K.O.'d if it loses a battle it is attacked in or an effect K.O.s it.
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