Karaten

Karaten 「カラテン」, or empty tenpai, is a tenpai hand that cannot win because all possible winning tiles are unavailable. The "visible tiles" may either be discarded, used as a dora indicator, and/or already exist in one's hand. In addition the tiles may be held in other players' hands or in the dead wall, but these would be unknown to the player.

Example of a karaten riichi, with all waiting tiles circled in red.

Karaten tenpai acquired after calling kan.

Karaten situation, where the winning tiles to a hadaka tanki were called for pon earlier.

Karaten hands are generally considered tenpai for the purpose of ryuukyoku, except if all four copies of the winning tile are in the player's own hand.

The fifth tile case

When a hand has all four copies of a tile, and is waiting on a fifth copy of a tile, it may not considered tenpai at all. Example:

Waiting for: (impossible)

If this hand could obtain a fifth 5-pin, it could win by completing a triplet and pair.

Waiting for:

Similarly, this hand could complete a sequence if there was a fifth 3-pin, but all four are part of a kan.

This is subject to rule variation. In some platforms, hands like these still count towards tenpai.

Cases

• On Ron2, there has been an instance of a person being able to call riichi with a gutshot wait shape for a 6-pin when they have made a closed kan of 6-pin already. The hand was considered noten, but did not trigger a chombo penalty (mainly due to programming assuming no one could do something that could be viewed as faulty). The hand was not in a valid tenpai shape when it came to scoring a drawn hand, but not okay for determining if a player was legally allowed to declare riichi.
• On Tenhou, there have been reports of a hand containing 12s44466688p with a kan of 3s, scored as in tenpai.
• Likewise, the same kind of case is allowable in Mahjong Soul.