Irezumi (入れ墨, literally translates to 'inserting ink')
It is the Japanese art of tattooing, which is heavily associated with the Yakuza. It can be anywhere on the body, but is commonly done on the back. It is not uncommon for the tattoo to expand from the back to cover other parts of the body, such as the thighs, buttocks, or, in the rare instance, the entire backside of the individual.

Irezumi is distinct from typical tattooing in part because it is applied entirely by hand, even in modern day, making the process a long and arduous one.