Yubitsume (指詰め) is a kind of minor amputation; the removal of finger joints. Yubitsume is considered the most sincere of apologies and more prevalently done by a lesser Yakuza when he or one of his proteges has done something to offend the gang's Kumicho.
Due to the restrictive social stigma placed on people in Japan who appear to have performed yubitsume, the practice is becoming rarer to see in younger generations of Yakuza. People who have performed yubitsume and leave organized crime often have a difficult time transitioning into normal life. Several organizations have set up prosthetic fingers for yakuza who have amputated all or part of their fingers to maintain a normal look for rehabilitation.
In Ichi The Killer the Yubitsume ritual is modified by character Kakihara (Tadanobu Asano), who asks forgiveness from the Kumicho of his Gumi by removing the tip of his tongue, complete with tongue rim piercing.
Yubitsume's origins are largely credited to the bakuto, who would accept part of a finger to cover a gambling debt. The pinky on the left hand was chosen because it would impair the swordsmanship of the offender.
The ritual calls for a small, clean (usually white) cloth to be laid down. The offender places their hand on the cloth palm down. Using a very sharp knife, they then cut off the left pinky above the top knuckle. This piece is then wrapped in the cloth and offered to their kumicho/oyabun (boss). Further infractions will remove another section of the pinky, and so on.